Add support for a reverse proxy that handles multiple domains via different
web roots (http[s]://proxy.tld/domain.tld/owncloud).

As the reverse proxy web root is transparent for the web server the
REQUEST_URI and SCRIPT_NAME need manual adjustments. This patch replace
the direct use of this _SERVER variables with function calls and extend
this functions to overwrite the web root. Additionally it adds a Sabre
request backend that extends the Sabre_HTTP_Request to use the same
functions.

LDAP: support for multiple LDAP/AD servers

Improved appsmanagement

small visual improvements

increase opacity of buttons, fix for dark backgrounds like header in pub...

Trash bin

Search display name and uid

search for display name and uid (with no display name) since it is possible that not all users have a seperate display name