Allow saving incomplete external storage config

Use `file_exists` to verify that config file exists

Add value if restore of data is possible for a user

This is needed for Dropbox and others that need a token.

Because setStorageId now instantiates storages, they might throw
exceptions if arguments are missing.

This fixes the unit test to not throw exceptions and have their default
config arguments set.

* reason: nice to know before password change in user management
* restore is possible:
	* encryption is disabled
	* encryption is enabled, admin and user has checked the
	  restore option
* if not possible:
	* highlight users row in red once the admin wants to change the password
	* show also a little tipsy

disable the app code checker - some previous shipped apps cannot be inst...

Fix node interface

Disable JS plugin for sharing in public mode

Only reload file list after remote share accept request returns

disable the app code checker - some previous shipped apps cannot be installed from the appstore now :facepunch:

Make error more descriptive

There might be the case that `fopen($file, 'r')` returns false and thus ownCloud might believe that the config file is empty and thus potentially leading to an overwrite of the config file.

This changeset introduces `file_exists` again which was used in ownCloud 5 where no such problems where reported and should not be affected by such problems.

Ref https://github.com/owncloud/core/issues/12785#issuecomment-71548720

Ref https://github.com/owncloud/core/issues/13693#issuecomment-71546767

When accepting a remote share, an ajax request is sent to the server.
Only once this request returns should the file list be reloaded.

This removes the logic that registers the share action and modifies the
rows. Share actions aren't needed in the public file list.

use uid provided by setupfs hook to mount server2server shares

Prevent double slash in shareinfo request URL

certificate manager should always use a \OC\Files\View otherwise we will get problems for different primary storages

use uid provided by setupfs hook to mount server2server shares, otherwise mount will fail for public link shares

Remove duplicated definition of APIController

Add a method to set/unset multiple config values with one write

by default send mail for new server-to-server share

Don't check for `always_populate_raw_post_data` on HHVM

Do not retrieve shares through group if user has no group

HHVM seems to have problems with this at the moment (even setting those values in the php.ini of HHVM doesn't have helped much) and thus the unit test execution failed.

So it's better if we disable this check for now for HHVM.