Fixes #6097,bz1120427 - repository.feed -> repository.url

Migrating a repository data model attribute from feed to url. The word
feed applies to the feed url used by pulp, but in katello UI, CLI and
API we consistently use url for feed. To mitigate this confusion it was
deemed to rename feed to url.
Fixes #6894,bz1123473 - rm sys from HC docs

Remove references to system in the host-collection api documentation
fixes #6913 / BZ 1092143 - content view version - disable promote/remove on failed task

This commit will disable the promote/remove button for a content view version,
if the current task being executed resulted in in an error.  Once the error
has been resolved and the task completes, the buttons will be re-enabled.
fixes #6883 - reverse order of activation keys
Merge pull request #4520 from dustint-rh/host-collection-doc-text

Fixes #6894,bz1123473 - rm sys from HC docs
Merge pull request #4448 from parthaa/feed-to-url

Fixes #6097,bz1120427 - repository.feed -> repository.url
Merge pull request #4526 from thomasmckay/6883-actkey-order

fixes #6883 - reverse order of activation keys
Merge pull request #4523 from bbuckingham/issue-6913

fixes #6913 / BZ 1092143 - content view version - disable promote/remove on failed task