Allow region override for url_for

If region is passed in to url_for use that, otherwise continue
to use the region from the user's session.

Fixes bug #1231171

Change-Id: Ia7d2a4f12a3c0d4d45bb918255184d1736f5bddf
Allow to specify custom horizon.tables.DataTable template

This fix allows user to provide his own template in Meta inner
class of DataTable's subclass (and thus extend or completely
override the default 'horizon/common/_data_table.html' template).

Change-Id: I1d1a7b2bf74dcaaee7a7096521853920feb40b21
Closes-bug: #1233609
Fix typos: "gruop" and "remove from"

Change-Id: If1afd82ffff3f4058c87b675913d4a0d31c52c09
Closes-Bug: #1234119
Merge "Allow to specify custom horizon.tables.DataTable template"
Merge "Fix typos: "gruop" and "remove from""
Merge "Allow region override for url_for"