Use pointers in the image client interfaces & api.
Merge pull request #71 from ncdc/image-client-pointers

Merged by openshift-bot
WIP Card#287 - Allow git webhooks to trigger build on git push
WIP Card#287 - changed the webhook mgmt, added git webhook implementation
WIP Card#287 - Changed plugin registration mechanism, now plugin is registered
manually inside cmd/master/master.go along side with installing the REST API.
Changed GetBuildFromPlugin method name and other house cleaning.
WIP Card#287 - Changed controller registration, moved gitwebhook to github package,
moved test files to gitub/fixtures dir, removed unnecessary elements from github
types.go, renamed types.go -> types_v3.go.
Rebased and added build integration, extended tests as well.
WIP Card#287 - added:
- json/yaml tag for secret
- client.Client & client.Fake takes and returns pointers
- fixed webhook registration in master.go
Card#287 - Refactored controller, completely removed webhook.go