More themable strings

This is quite a hefty piece and I’m not a PHP dev, so please review and test thoroughly.

* split getName and getTitle so we can have »ownCloud« and »ownCloud Enterprise Edition« as separate strings.
* fix image alt tags using "ownCloud" and replace it with the themable strings
* reword WebDAV auth to not have "ownCloud"
* reword LDAP config partly and also use the themable strings
* simplify Export on admin page, do not use "ownCloud", also preselect first entry to prevent error when clicking »export« button without having anything selected
* also use themable strings for installation – please test this extra good!

And don’t even think about backporting this.

@DeepDiver1975 @karlitschek @schiesbn @VicDeo @icewind1991, and @blizzz for the LDAP page.