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.
I think we could do that. Implementation with __getattr__ is good because it produces less code and makes it really fast, because we cache all plugin functions as methods in debugger object and have no overhead on dispatching. But true it adds a portion of magic to the code and it could be avoided.