Fixes https://github.com/owncloud/core/issues/11239

Fix issue where the currently logged user was causing side-effects when
upgrading.
Now setting incognito mode (no user) on update to make sure the whole
apps list is taken into account with getEnabledApps() or isEnabled().

OC_Util::sanitizeHTML() also supports array but we actually had no unit test for it. Additionally this commit introduces a test for escaping " into "

- added PHP utility function to check for file name validity
- fixes issue where a user can create a file called ".." from the files UI
- added extra checks to make sure newfile.php and newfolder.php also
  check for invalid characters

In environments where there are rules for the email addresses, the "from
address" that owncloud uses has to be configurable.

This patch adds a new configuration variable 'mail_from_address'.
If it is configured, owncloud will use this as the sender of *all*
emails. (OwnCloud uses 'sharing-noreply' and 'password-noreply' by
default). By using the 'mail_from_address' configuration, only this
email address will be used.

When accessing a shared folder, the folder's owner appears as mountpoint
but wasn't wrapped by a quota storage wrapper.

This fix makes sure that all home storages are wrapped by a quota
storage wrapper, if applicable, to make sure quotas are respected when
uploading into shared folders.

 - Use camelCase

 - Add some phpdoc

 - Fix some indents

 - Use some more spacing

Unittests for:

- search/result

- util

- preferences

instanceid is generated by uniqid() and then used as the
session_name. Because session_name requires at least one letter
and uniqid() does not guarantee to provide that, in the case that
uniqid() generates a string of only digits, the user will be stuck
in an infinite login loop because every request will generate a
new PHP session.

Move testcase for getDefaultEmailAddress with mail_domain set in config.php to own test function.

see #2499