Fix collision on temporary files + adjust permissions

Block old legacy clients

fix encryption header error

testRewind tests reading and writing after rewind on an encrypted stream; testWriteWriteRead tests r+ mode

When moving back the pointer to position 0 (using stream_seek), the pointer on the encrypted stream will be moved to the position immediately after the header. Reading the header again (invoked by stream_read) will cause an error, writing the header again (invoked by stream_write) will corrupt the file. Reading/writing the header should therefore happen when opening the file rather than upon read or write. Note that a side-effect of this PR is that empty files will still get an encryption header; I think that is OK, but it is different from how it was originally implemented.

[encryption] fix moving files to a shared folder

Ignore test folders when checking the code for compliance

Tear down FS after running trash expire

Show hint if there is no delete permission

Add missing loading indicator for enabled apps

Issue 15804 occ user delete exception

* add class .no-permission which shows the default delete icon
* fixes #15172
* add unit test for no permission and for delete permission

* happened when an app gets activated, because the
  new appended HTML doesn't contain the loading
  image
* fixes #15806

In case of an not sent UA header consider the client as valid

Fix webdav access for public reshare

This changeset hardens the temporary file and directory creation to address multiple problems that may lead to exposure of files to other users, data loss or other unexpected behaviour that is impossible to debug.

**[CWE-668: Exposure of Resource to Wrong Sphere](https://cwe.mitre.org/data/definitions/668.html)**
The temporary file and folder handling as implemented in ownCloud is performed using a MD5 hash over `time()` concatenated with `rand()`. This is insufficiently and leads to the following security problems:
The generated filename could already be used by another user. It is not verified whether the file is already used and thus temporary files might be used for another user as well resulting in all possible stuff such as "user has file of other user".

Effectively this leaves us with:

1. A timestamp based on seconds (no entropy at all)
2. `rand()` which returns usually a number between 0 and 2,147,483,647

Considering the birthday paradox and that we use this method quite often (especially when handling external storage) this is quite error prone and needs to get addressed.

This behaviour has been fixed by using `tempnam` instead for single temporary files. For creating temporary directories an additional postfix will be appended, the solution is for directories still not absolutely bulletproof but the best I can think about at the moment. Improvement suggestions are welcome.

**[CWE-378: Creation of Temporary File With Insecure Permissions](https://cwe.mitre.org/data/definitions/378.html)**

Files were created using `touch()` which defaults to a permission of 0644. Thus other users on the machine may read potentially sensitive information as `/tmp/` is world-readable. However, ownCloud always encourages users to use a dedicated machine to run the ownCloud instance and thus this is no a high severe issue. Permissions have been adjusted to 0600.

**[CWE-379: Creation of Temporary File in Directory with Incorrect Permissions](https://cwe.mitre.org/data/definitions/379.html)**

Files were created using `mkdir()` which defaults to a permission of 0777. Thus other users on the machine may read potentially sensitive information as `/tmp/` is world-readable. However, ownCloud always encourages users to use a dedicated machine to run the ownCloud instance and thus this is no a high severe issue. Permissions have been adjusted to 0700.Please enter the commit message for your changes.

update icewind/smb to 1.0.1

Delete temp files after testing encryption stream wrapper

Checks if getenv returns proper system environment variable results

Only get encryption status when logged in