Fix Tags Block Save in Stacks Dashboard Page

Fix tags blocks save in stacks dashboard page.

Block does not save propertly when in stacks dashboard page as blocks
are unable to save to the page based on `$_REQUEST['cID']` as they are
expecting to be in a page not a dashboard dialog.

- Check for being in the Stack Dashboard page and display accordingly
- Do not show tag attribute form in add / edit in dashboard page
Merge pull request #1535 from mkly/fix_tag_block_save_stacks_dashboard

Fix Tags Block Save in Stacks Dashboard Page