Respect declared "name" from addon-info.json
Handle special case for symlinked plugin w/o "name" getting both names
Rename s:custom_name_locations and improve comments
Rename s:custom_name_locations to s:plugins_by_location

Also store all plugins unconditionally, not just plugins with special
locations, and update comments.
Merge pull request #44 from google/addon_name

Respect plugin name from addon-info.json