Refactoring for moving IndexAdapter into addon.

We want to move Index-Adapters from the deployinator project
into the ember-deploy addon directly. This is the start and
necessary groundwork for this transition.

* Registry now supports index-adapters.
* Cleanup of AssetsUploader/-adapters.
Add revision upload via Redis-Adapter.
Add redis to travis.yml.

We want to test redis integration so we need to tell
Travis to boot redis on startup.
Finish Redis-Adapter.
Use ember-deploy adapters for index/list/activate.

We can now remove the dependency on the deployinator project
because handling the key/value-store updates is handled by
the index-adapter layer since the last commits.

I also added the notion of revision taggers. Which in the future
should also be pluggable. Currently there is only one sort of
revisionTagger and that's the `sha` tagging adapter.

* remove deployinator dependency.
* add revisionTagger.
* refactor index/list/activate tasks.
Update: Adapters are now responsible for logging.

Adapters should do all their logging on their own because
useful log messages depend on what the adapters are doing.

* Refactored the redis adapter to output logs directly.
Try to fix Travis npm issue.

Travis seems to have troubles with `npm install` from
time to time. This should fix the issue.

Github comment for reference:
https://github.com/travis-ci/travis-ci/issues/2244#issuecomment-55473829
Allow adding adapters via ember-cli-addons.

We want to support community and project specific adapters
which can now be added separately via ember-cli-addons.

* merge addon adapters into adapter registry on init.
Pass project to AdapterRegistry lookup in tasks.

We need this to use the newly added project specific
adapters feature.
Update README with custom adapter documentation.

* add documentation on how to write custom adapters.
* restructuring README.