Added support for extra backends

Somebody had forgotten "OC_User::setupBackends();"...
Added ownCloud backend for external storage

To make it possible to use the short ownCloud URL (without specifying
webdav.php or remote.php), a new backend is available for ownCloud.

The user must specify the host + context path in the "Url" field (which
is mapped to the "host" parameter) and the subdir to mount in the "Root"
field.

This is to prevent confusion because some users forget to append
webdav.php or remote.php to the WebDAV URL.

Fixes #4923
No decimal points for Kilobyte and Byte #5371.
#6051 [ux][files] Move File Spinner

Added spinner to file icon when moving to new folder or out of folder.

Commit is related to #6051
Fixed indention.

As per @kabum request, indention on line 694 has been fixed.
Fixed Dropbox/Google storage async save call

When clicking "Grant access", the settings for Dropbox/Google were saved
through a call that gets cancelled when redirecting to the grant page
(for example in Firefox)

This fix makes sure the "save settings" call finished before redirecting
to the grant page.

Fixes #6176
change mail address by pressing enter - fixes #6179
fix typo
Moved content disposition code+workarounds to OCP\Response

Added new OC\Response API called setContentDispositionHeader() that
contains the needed workarounds for UTF8 and IE.

Refactored download code to use the new API.

Removed unused trashbin download file.
Added workaround for Android content disposition

Fixes #5807
Fixing Issue #6301 on master branch
Added private var $certPath to store the user root cert

Move logic to determine the $certPath path to the constructor and modify to get the path from OC_User::getHome()

Add curl options to use the certificate to avoid certificate errors with self-signed certicates in the downdload/upload method so we don't get blank files
Fixing tab/space coding style
Only set SSL things when ```$this->secure``` is ```true```
Fix ```createCertificateBundle``` and  ```getCertificates``` methods
from ```OC_Mount_config``` to use ```OC_User::getHome``` to get the
path
fix the config option to remove the ability for users to set their displayname
Replace static usage of OC_Config and OC_Preferences with the injected \OC\ConfigAll
spaces to tabs
Merge branch 'master' into user-no-change-displayname
Enforce required phpunit version

This will prevent frustration and confusion when unit tests fail because
the wrong phpunit version was used
Added isUserAgent() method to request

- added isUserAgent() method to OC_Request which makes it possible to
  test it
- OC_Response::setContentDisposition now uses OC_Request::isUserAgent()
Added test cleanup listener to detect untidy tests

After each test suite, detects whether there are stray datafiles, hooks
or proxies, then show a warning and clear them.