Manage Image Tags

Summary
=======
Horizon should provide UI to update and delete image tags.
Display the tags associated with a particular image in the overview of that image.

Motivation
=========
Currently there is no way to manage image tags from dashboard. It would be nice for user to have UI to manage the image tags.

Description
==========
There must be option to update and delete tags in the edit image dialog in the image overview.
The tags associated with the image must be visible to the user in image overview.

The CLI gives the following output on image-show
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| checksum | ee1eca47dc88f4879d8a229cc70a07c6 |
| container_format | bare |
| created_at | 2016-08-29T05:06:44Z |
| disk_format | qcow2 |
| id | 017059ce-c85a-46c1-90e3-aaea8deca230 |
| min_disk | 0 |
| min_ram | 0 |
| name | cirros |
| owner | ac6b358caea24e4cb4ec45a2481ab4df |
| protected | False |
| size | 13287936 |
| status | active |
| tags | [] |
| updated_at | 2016-08-29T05:06:45Z |
| virtual_size | None |
| visibility | private |
+------------------+--------------------------------------+

The dashboard is also expected to be in sync with the CLI output.