Refine entry publication quota

The previous approach prevented published entries from being updated
when the published entries quota was exhausted. Instead we need to
check whether the quota would be exceeded under the assumption that
the current entry was published. As a side effect, published entries
cannot be updated if the quota already is exceeded, which is the
desired behaviour.

To come up with a sensible ui, the editor now requires information
about both the current and the assumed state of the quota. Therefore,
the generic `editor/quotas/:name endpoint` has been replaced by a
dedicated `entry_publications` endpoint which supports both checking
whether the entry can be published and performing the publication.

* add EntryPublication poro to encapsulate publication logic
* add EntryPublicationsController to check and publish entries
* add EntryPublication Backbone model
* turn generic QuotaDecoratorView into
  EntryPublicationQuotaDecoratorView
* make PublishEntryView use EntryPublication Backbone model
* remove Editor::QuotasController
* remove RevisionsController#create which is now handled via
  EntryPublications#create
* add verify_not_exceeded! method to Quota class
allow previewing draft revision
register page type view helpers with RevisionsController
Allow to scope entries by request attributes.

Adds a public_entry_request_scope configuration setting which allows
restricting the avaiable published entries under a specific host. For
example, the entries accessible under an account's CNAME can be
restricted to those of the account.
fix colored area behind loading spinner on startup
extract account show template from admin to multiple partials
Merge pull request #64 from upsworld/cm-loadingSpinner-fadeIn

fix colored area behind loading spinner on startup
Merge pull request #62 from tf/preview

Entry Preview
Merge pull request #60 from tf/publish-quota

Refine Entry Publication Quota
Merge pull request #61 from tf/request-scope

Allow to Scope Entries by Request Attributes #61

Adds a public_entry_request_scope configuration setting which allows
restricting the avaiable published entries under a specific host. For
example, the entries accessible under an account's CNAME can be
restricted to those of the account.

Conflicts:
	CHANGELOG.md
Merge pull request #65 from g-w/gw-account-admin

extract account show template from admin to multiple partials
restructure changelog
Namespace model name translations (fixes #58)

* Replace "account" with "pageflow/account" and so on in
  activerecord.yml.
* Also supply aliases for non namespace variant.
  ActiveAdmin skips module names since we register admins with
  `as: "Account"` option to get routing right.
Make jQuery gem dependencies more specific

ActiveAdmin only depends on jquery-ui-rail >= 4.0 but breaks with
version 5.0.
update Gemfile.lock
Merge pull request #66 from tf/model-name-translations

Namespace model name translations (fixes #58)
Merge pull request #67 from tf/jquery-rails-version

Make jQuery gem dependencies more specific (fixes #63)
bump version to 0.2.0 and finalize changelog
update Gemfile.lock