swallow exceptions when generating thumbnails

Merge branch 'feature/cale/cms-master' of github.com:MITx/mitx into fix/cdodge/cas-thumbnail-exception-handling

Feature/cale/cas import ui

removed red import button – drawing too much attention; this will be reworked onto a different page at some point anyways

styled edge registration form

DraftMongoContentStore needs to both delete the draft *and* the non-draf...

Feature/cale/edge landing page

per feedback, change back 'draft-aware' modulestore to not delete the published copy. In delete_item in views.py do the logic to determine whether we should be using a 'draft-aware' modulestore or not, based on the category type

allow importing of .tar.gz packages of courseware

Edge landing page, styled, not wired up yet

Feature/cdodge/cms import

various style updates

Fix/cdodge/cas bugs

fix up dev.py to include the new flag

Fix regression on creating new sections and subsections. They were being set into 'draft' when we are not currently supporting draft modes for those areas of the hierarchy