Add dropdown actions to detail page

Add support for performing actions on an object from the object's
detail page. Actions are displayed in the page header, in a
dropdown menu. As a POC, this patch enables dropdown actions on a
detail page of a volume (/project/volumes/volume-id/).

Partially implements: blueprint detail-pages-ia

Change-Id: Ie21c63d86c2806d9689ae7f1a67b67c83710c108
Add dropdown actions to all details pages

Partially implements: blueprint detail-pages-ia

Change-Id: Ic09385d19b417b256cbc51d044d66ecbb54c7d52
Add support for row actions to detail pages

Add support for performing actions on an object from the object's
detail page. Actions are displayed in the page header, in a
row of buttons. To use this newly added capability, `row=True`
must be passed as a parameter to the render_row_actions method,
when called from a DetailView.

Change-Id: I4fd96433f9514242c21d6c47f79bf83f3a5e4fc0
Implements: blueprint detail-pages-ia