Adds system preferences to template context

It's now possible to use
  $gimme->getSystemPreference(preferenceName, defaultValue)
in the templates. For preference names the machine names should be
used. The default value will be returned if the preferences it not
set.
Merge pull request #899 from m038/CS-5584

Adds system preferences to template context
Merge branch 'v4.3' of git://github.com/sourcefabric/Newscoop into v4.3
CS-5558 Add dlg files for campsiteimage plugin and correct locale values