Fixes issue #292 (Dashboard Re-skin: System and Settings > Permissions and Access > Maintenance Mode)

Hi all.

New to GIT so there may be some problems with this PR. I couldn't find out how to attach a PR to the issue itself.  If this is OK, I can carry on looking at the other interface changes but I'll wait for feedback from people that know more about core edits incase I've done something wrong. 

Andrew wanted the bold on the label removed as well (https://github.com/concrete5/concrete5-5.7.0/issues/292), that's set in app.css which I haven't modified as I know nothing of LESS/SASS/whatever the new CSS technology is of today. 

I messed up and removed the security token and didn't realise until testing. Re-added in the third commit. 
Thanks.
J.