Simple Plugin system for Javascript
Log exceptions in DAV storage

In some cases a "NotFound" might be expected, so just return false as
before. But for other exceptions, the exception is now logged.
Use UID instead of login name

Login name can be something different and thus I'm pretty sure this will break in combination with external auth providers such as LDAP.
remove triggerupdate, ref #11872
add quiet option, ref #8794
Remove obsoleted filelist prototype backup in tests
return correct result
Expose backend type via REST API

This change will expose the user backend via the REST API which is a pre-requisite for https://github.com/owncloud/core/issues/12620.

For example:
````json
[{"name":"9707A09E-CA9A-4ABE-A66A-3F632F16C409","displayname":"Document Conversion User Account","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/9707A09E-CA9A-4ABE-A66A-3F632F16C409","lastLogin":0,"backend":"OCA\\user_ldap\\USER_LDAP"},{"name":"ED86733E-745C-4E4D-90CB-278A9737DB3C","displayname":"Hacker","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/ED86733E-745C-4E4D-90CB-278A9737DB3C","lastLogin":0,"backend":"OCA\\user_ldap\\USER_LDAP"},{"name":"71CDF45B-E125-450D-983C-D9192F36EC88","displayname":"admin","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/71CDF45B-E125-450D-983C-D9192F36EC88","lastLogin":0,"backend":"OCA\\user_ldap\\USER_LDAP"},{"name":"admin","displayname":"admin","groups":["admin"],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/admin","lastLogin":"1418057287","backend":"OC_User_Database"},{"name":"test","displayname":"test","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/test","lastLogin":0,"backend":"OC_User_Database"}]
```
Make class compatible
Add a DateTimeFormatter class which allows overwriting the language and timezone

Fix #12227
Add sometests and copy tests from Util::formatDate to new class
Add newline that was removed by 15be763d46d56c57d4f0def7745bb02d513e3a38
cleaning up the build directory
make path absolute
Update 3rdparty to add PEAR.php back
Merge pull request #12737 from owncloud/fix-missing-nl-phpstorm

Add newline that was removed by 15be763d46d56c57d4f0def7745bb02d513e3a38
Merge pull request #12711 from owncloud/add-backend-to-rest-index

Expose backend type via REST API
Deprecate Util::formatDate()

Make DateTimeFormatter a service and adjust tests that have been inaccurate
Require the interface and return a string instead of private classes
Add filter for 'backend' to user REST route

This adds a "backend" type filter to the index REST route which is a pre-requisite for https://github.com/owncloud/core/issues/12620

For example when calling `index.php/settings/users/users?offset=0&limit=10&gid=&pattern=&backend=OC_User_Database` only users within the backend `OC_User_Database` would be shown. (requires sending a CSRF token as well)

Depends upon https://github.com/owncloud/core/pull/12711