Display landing page when blog slug is missing

When a site has a single blog and no blogslug is specified in the url
then dispaly the landing page of that blog.
Added validation for slug field in blog change form.
Merge branch 'master' of github.com:laurafeier/django-cms-blogger
Merge pull request #11 from laurafeier/LUN-1446-landing-page

Display landing page when blog slug is missing
Fixed messages misspelling.
Removed validation for entry title on form. Slugs will get generated automatically and they should be unique.
Merge pull request #12 from laurafeier/LUN-1507

Lun 1507
Changed categories for promo plugin to be saved as string since multiple blogs can have the same categories names and they will all show up in the choices.
Move social tracking to js (wasn't working for promotion plugin), fix 2 windows opening for twitter tweet