Dynamically discover requirements files
Initial parts of Bitbucket importing
Add automatic documentation type choosing
Add “basic” concept to builders, on basic imports.
Specific modeling for BB
Default to auto discovering of doc type
Add initial build signals
Auto build new tags when pushed.

Add tests for this and the stable version code.
Fix version arg
Merge branch 'add-build-signals' into project-onboard-improvements

Conflicts:
	readthedocs/projects/tasks.py
Remove token passing
Merge branch 'project-onboard-improvements'