Move Django template debugging to a separate plugin. Added Jinja2 template debugging.

This is 
a) refactoring of tracing, that moves all Django related code to plugin that is enabled on respective breakpoint add and 
b) Implementation of Jinja2 template debugging ontop of the new plugin architecture.

The resulting tracing speed should remain the same(we have measured performance of this new version) while code readability is increased by decoupling from Django tracing parts.

Patch authors: Elizaveta239 and traff

Known issues: set attribute is not implemented yet for Jinja2 and broken for Django, we will fix it afterwards.
Humm... this seems like a smell for me... the user can't have 2 active plugins?