Shows a warning message when deleting a container that contains data.

We cannot delete objects in the container since there may be millions
of objects in that. The batch deletion should be done in swift instead
of Horizon. The batch remove of objects function is only in swift CLI
command now. This commit replace the unclear message with a warning
message that tells the user the container is not empy.

Related bug: https://bugs.launchpad.net/horizon/+bug/1034890

Fixes bug: #1096084

Change-Id: I59b46a3535b8654734c3dae4eec916ab1b53c716
Refactored the templates code

Created generic template _workflow_base.html
in horizon/templates/horizon/common folder
with 'workflow.name' to replace multiple nearly
identical templates with different titles.

Implements blueprint dry-templates

Change-Id: Ieb14e263381020ed6604149ff9295f8cc814a9e6
Merge "Refactored the templates code"
Merge "Shows a warning message when deleting a container that contains data."