Adding attribute schema class for attributes

This patch introduces simple schema class for attributes.
There are two options avaliable for this schema:
 - description
 - support status
It gives ability for adding support status for each attribute.

Change-Id: I46cbf776f315cbe6414005cbee65da1cefdc5f7d
Closes-Bug: #1305584
Merge "Adding attribute schema class for attributes"