WIP
Remove checks for uninstall for now.
Lookup shadow tree root using a zca utility and tidy up.
Uninstall now works.
Use a site local utility registered via GS componentregistry.xml in order to manage the shadow tree.
Merge remote-tracking branch 'origin/master' into uninstall-profile

Conflicts:
	buildout.cfg
	src/experimental/securityindexing/benchmarks.py
Force the DX benchmarks to run *before* the AT ones (by modifying the test names with prefixes A_ -> DX, B_ -> AT)
back to 100% coverage. benchmarks work too with a little encouragement.
Remove travis specific parts.
Opa. .coveragerc that was meant to skip bare assert statements was not running and assert* methods in unittests.
Update ignores.
Fix travis buildout to add download and install back in. (extends issue).
Remove obsolete TODO entry.
Remove uneccessary addition of mock egg to test part.
Formatting.
Add mkrelease part.
Re-worked benchmark parts such that we have one runnable per content type system.
Corrected github url.
Tidy up.
Be explicit about strings
Document the purpose of having old z2 style initializer.
Add z2 product registration.
Add comment to utility declaration and removed provdided since we do its done in python.
Re-work test layer and cases classes so that benchmarks run cleanly with package un-installation.
Fleshed out interfaces.
Added marker interface for shadowtree root node.
Update shadowtree tool to use the correct interface.
Added methods to IShadowTreeTool to allow for package uninstallation via Extentsions.Install.
Added package stanza for Extensions.