Misc: misc. changes to imagex_blog view

## Ready State: Yes

The new imagex_blog content pane allows filtering by tag(s), if a tag isn't present in the system it would show a "term not found" error, this settings tweak prevent the error showing.

Also adds a empty text if no posts are found.

## Requirements & Dependencies

None

## Deployment Instructions

* Merge code.
* Enable module `imagex_blog`
* Clear caches with `drush cache-clear all`

## Usage/Test Instructions

* Create some blog posts, tag them in the tags field
* Using panelizer add a new "Blog List Pane" and ensure that filtering for a tag/term that doesn't exist does not show any error message