Update CodeMirror directory
Fixes #1853 Allow login via email and/or username with settings in the ACP
Also added some missing messages
Proper XML result validation
Remove unused/undocumented export feature
Remove unused/undocumented XMLHTTP location
Update "What's next?" message in installer
Add .thead_right and .thead_left classes

When you have two columns with two .theads the CSS3 border radius rounds the inner corners which is not desirable.
Add 24 hour lock to admin log

To prevent recent actions being wiped by unauthorized people, add a lock to the admin log which prevents logs less than 24 hours old from being pruned.
Add 24 hour lock to moderator log

To prevent recent actions being wiped by unauthorized people, add a lock to the admin log which prevents logs less than 24 hours old from being pruned.
Use relative time for moderator logs
Remove deprecated <font> tag
Update attachtype images
Replace gif image references with png
Add mobile detection to the ACP

This functionality was half implemented so I went ahead and added a simple mobile detection function.
Fix mobile detection in the ACP
Add `useragent` column to mybb_adminsessions

It seems I may have slipped up.
Don't set $user_type after mobile detection
Add missing line of code
Fixes #2250 Admin Log errors