Fixed issue if display language and installed language differ

WCFSetup uses de, but only en is installed.
Updates Font Awesome to version 3.2.1

Closes #1493
Removes RELATIVE_WCF_DIR in language items
Fix duplicate class="" attribute
Work-around for disable i18n with only one language installed
Fixed master password path
Properly supporting single-language setups
Removed InnoDB-warning from ACP index page
Merge branch 'master' of github.com:WoltLab/WCF