Correctly use Rope's project API

[JulianEberius]

SublimeRope should use Rope's API more correctly. It should keep one project open in memory for all views of one ST2 project (or window) and use its report_changed, validate etc calls consistently. The global and project module cache should have a unified interface (only one command to regenerate) for SublimeRopes user, and cache rebuilds for the global cache could be triggered automatically when the settings change etc etc.

I'll start working on these changes myself, as I have some time, but I wanted to record them here.