Reverted usage of pack()

The PHP documentation lies, 'a' and 'Z' do NOT behave the same for pack() (but they do for unpack()).
Small style optimization
Fixed invoking of singleton methods
Merge branch 'master' of github.com:WoltLab/WCF
Fixed notifications
Updating minified JavaScript files
Fixed hidden input fields not being submitted in search
Updating minified JavaScript files
Fixed encoding issues with tags
Updating minified JavaScript files
Adds explicit validation of recent activity object type

… which creates a proper error message instead of an database exception.
Fixed relative time format
Merge branch 'master' of github.com:WoltLab/WCF
Updating minified JavaScript files
Fixed quote error on quick reply
Merge branch 'master' of github.com:WoltLab/WCF
Updating minified JavaScript files
Fixed typo
Merge branch 'master' of github.com:WoltLab/WCF
Small style optimization