Removed LOLCAT locale - sadly not supported by our translation infrastructure

It breaks the CMS when selected. If there's interest in maintaining it,
we can re-add. Fixes https://github.com/silverstripe/sapphire/issues/1457
Better error message when attempting to enter a blank URL Segment (fixes silverstripe/silverstripe-cms#1570)
BUGFIX Use onadd instead of onmatch on cms-add-form when creating new page #673
Merge pull request #678 from patbolo/bugfix-673

BUGFIX Use onadd instead of onmatch on cms-add-form when creating new pa...
FIX Use SSViewer.theme_enabled in CMS logic
Update pl_PL.js
Merge pull request #676 from kinglozzer/urlsegmentfield-error-fix

Better error message when attempting to enter a blank URL Segment (fixes silverstripe/sapphire#1570)
Fixed behat tests
Merge remote-tracking branch 'origin/3.0' into 3.1
MINOR: added translation for children list and added tree translations
Merge pull request #679 from ARNHOE/3.1

MINOR: added translation for children list and added tree translations