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'm Ok with having this, but the way it's implemented to keep this count isn't really ok for me... mostly, it currently uses symmetry of commands (i.e.: add breakpoint means +1 and remove breakpoint means -1), but I think this can be error prone -- if the client for some reason adds some breakpoint twice it'll be wrong, or if it removes a breakpoint that didn't exist in the first place we'd have the same problem). We already have a step to consolidate the breakpoints, so, I think this should be done at that point -- or we could ask plugins if they have some breakpoint active and set that as a boolean accordingly.