Remove contrib.export app.

Fixes #196
Remove contrib.ajax (#217) and contrib.scheduler (#282)

Remove these two contrib apps.

Branch: 217-282-remove-contrib-ajax-and-scheduler
Refs #229: Change layout-split-2.html and layout-split-3.html to use Bootstrap classes
Freshen AUTHORS file
Branch: release-0.12.0
Fix EmptyPage exception

Messagelog was throwing an EmptyPage exception when rendering its table using djangotables2.

Changed template to not try to generate a link to previous or next page when there's not one.

Branch: fix/emptypage-exception
Merge pull request #281 from rapidsms/remove-contrib-export

Remove contrib.export app.
Merge pull request #283 from rapidsms/217-282-remove-contrib-ajax-and-scheduler

Remove contrib.ajax (#217) and contrib.scheduler (#282)
Merge branch 'release-0.12.0' into fix/emptypage-exception

Branch: fix/emptypage-exception
Merge pull request #284 from rapidsms/fix/emptypage-exception

Fix EmptyPage exception
Merge remote-tracking branch 'remotes/origin/release-0.12.0' into feature/268-remove-rapidsms-tabs

Conflicts:
	rapidsms/templates/layout.html

Branch: feature/268-remove-rapidsms-tabs
Remove RAPIDSMS_TABS from tests/default.py
Branch: feature/268-remove-rapidsms-tabs
Start a doc page on how the frontend works. Document how to control the links at the top of each page.
Branch: feature/268-remove-rapidsms-tabs