Merged ModelBase from devmo and sumo apps and get rid of cache machine.

This is an important step to have a leaner caching setup.
Added new "memcache" caching backend to be used by Jinja2 and constance.

Removed settings_local.py based CACHES setting in favor of settings.py.
This requires an update of all local_settings.py in use!
Move PageMoveError into exceptions module.
Extended render_stale_documents task to use a task group for its subtasks.

That means we can set a lock at the start of the task and destroy it again once the whole bunch of tasks have finished.
Added a MemcacheLock utility.
Use memcache cache backend for the rebuild task.
Merged the obscure lib/utils.py with devmo.utils.
Fixed the tests for the rebuilding of documents.
Stop deprecation warning to show up.
Minor cosmetic fixes.
Removed rebuild_kb task.
Merge branch 'master' into cache-lock-task-signals
fix bug 1013888 - Add styling for blockquotes
Removing padding from transparent page buttons
Fix bug 998346: Rebuild source document JSON on translate.

This is slightly hacky and ends up duplicating code, but the way the
rendering and JSON building happens currently there seems not to be
another option to force-refresh the parent doc's JSON.
fix bug 1018888 - Ensure dates filter properly within the revision dashboard
Merge pull request #2444 from ubernostrum/translation-json-998346

Fix bug 998346: Rebuild source document JSON on translate.
Merge pull request #2423 from jezdez/cache-lock-task-signals

Re-enable memcache as a optional cache backend. Use it for locking.
Merge pull request #2437 from darkwing/blockquotes-1013888

fix bug 1013888 - Add styling for blockquotes
Merge pull request #2445 from darkwing/revdash-dates-1018888

fix bug 1018888 - Ensure dates filter properly within the revision dash
Merge pull request #2439 from darkwing/language-button-spacing

Removing padding from transparent page buttons