First step towards a configurable grid.
Allow choosing a grid system on the Cover Settings screen.
Use a real vocabulary to choose the grid system in the collective.cover admin panel.
Change GridPlug into a utility, so more grid system plugins can be registered in the system later on.
Rename GridPlug to Deco16Grid and fix a typo in a method name.
Add upgrade step to add grid_system registry record.
test_linkintegrity.py should not be executable
Test grid_system record. Uninstall it.
Test the grid system vocabulary.
formated -> formatted
Remove grid_system on uninstall.

We already had 'delete', but that is deprecated, but according to the comment still needed on Plone 4.2.
Set up second grid and use it in vocab testing.
Test layoutmanager_settings with two grids.
Rename test grid system to Bootstrap3.
Testing: rename TwoGrids to MultipleGrids.

We might add a third grid for testing or for real at some point.
Test whether the default grid and a custom grid generate the correct classes.
Prefer single quotes.
add changelog entry for grid change
Update imports to follow plone.api style conventions.
Follow plone.api conventions on imports and prefer single quote strings