Making Extensions private until I can figure out if we really need all that code to do overrides.

Feels like there is room for improvements at least...
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Added SlowRepositoryEngine: reads and write to repositories

SlowRepositoryEngine will be replaced by a cached version when git support is completed.
Added git dependencies already, which probably is not necessary.
Serializers could be factored quite heavily.
Merge branch 'master' of github.com:adept-dm/adept