Added stopPropagation() to dblclick handler

This is to address the issue of not being able to edit models emitted by CMSPlugins. Because the event was being propagated, the double-click essentially triggers editing of both the model and of the plugin. The resulting mayhem made it impossible to do either. This fix seems to allow the editing of the model, without preventing edits to the plugin (by double-clicking on something other than the model).

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Nicer deprecation for placeholder_tags

* Instead of breaking placeholder_tags, makes it warn.
* Documented the deprecation of placeholdr_tags
* Added a check to the `cms check` command to check for deprecations
* Added a test for the deprecation check
fixed Django 1.5 compatibility
Fixed wrong reference
fixed UnicodeDecodeError
fixed django 1.4 support
Merge pull request #2575 from mkoistinen/issue_2432_fix

Fix for issue 2432
Merge pull request #2579 from ojii/nicer-deprecation-of-placeholder-tags

Nicer deprecation for placeholder_tags