Add new core function to register custom image sizes
Set alt= attribute for featured achievement widget image
Disable paging on Featured Achievement widget query
Make featured achievement widget use get_posts instead of a WP_Query

For better query optimisation... the previous SQL query didn't have a
LIMIT.
Reorder parameters because I have an alphabetical order thing.
Add new photo grid widget

This brings the "Available Achievements" widget back from the 2.x
versions, under a different name.