removed field_file_attachment from blog , added to common_fields

## Ready State: (No)

This pull request is related to the following PR
*https://github.com/imagex/imagex_common_fields/pull/4

## Requirements & Dependencies
Removed file_field_attachment
Added reference to common_fields file_field_attachment (in related PR)
Updated feature description to match convention for others
Removed conflict with common features and tags

## Deployment Instructions

* Merge code.

## Usage/Test Instructions

Enable Blog, ensure content type is correct and file_field_attachment exists