'Stack Template' tab for Heat Stack Details page

Once you launch a stack from any template source (using raw data
or template file), there is no possibility to check this template
later from Horizon. This patch set adds 'Stack Template' tab to
Stack Details page.

Partially implements blueprint: heat-ui-improvement

Change-Id: I27fb687829f9c060ea55d81bcc0344a6e782da06
Merge branch 'master' of https://github.com/openstack/horizon