Fix typo in docstring: model_save -> save_model

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extra : source : 4da7933a346b3873738e57928394bd19e4d4a398
Implement a new can_move dynamic page permission

Content types can override can_move() to control whether a given page
move in the page tree is permitted. can_move() should raise a
PageMoveException if the move is denied. PageMoveException takes a
single argument: a message explaining the reason for the denial.

--HG--
extra : source : d1aed481293e8e327c0c98ace1a163ec7c0ba50b
extra : amend_source : 85942de580068bc3a40fbf6efc79c1e4275dd903
page tree: reload on move exception to revert the tree and display any messages

--HG--
extra : source : abce9c1f673a6c34556b203f50396c5e31be79ad
extra : amend_source : 421bd505fa9b6cab9950e3a0d5721c56c4243c65
Added quantifind.com to sites in README.
Added mezzanine.utils.html.thumbnails to RICHTEXT_FILTERS setting, which converts images within richtext fields into thumbnail references. Closes #567.
CSS fixes for send to twitter admin checkobx.
french translation correction
Document the can_move dynamic permission
french translation correction
Merge branch 'master' of github.com:lucmilland/mezzanine
Added Luc Milland to AUTHORS
Bump grappelli/filebrowser versions.
Faster admin left-hand menu animation
Show featured images in recent blog posts section.
Merge
Minor style tweaks to can_move page permission.
Version bump to 3.1.5
Added tag 3.1.5 for changeset 1536cfa7ef80
Update auto-generated changelog, docs, requirements.
README tweak