AssumeQuality plugin - default quality for tasks

Many releases no longer explicitly flag 720p, breaking quality filters or requiring complex manipulate setups. This allows a default quality to be applied to entries when none is found.

http://flexget.com/ticket/1498
Operate on individual quality components

Now applies defaults by quality component, so that defaults can be used even if other components are filled by the release.
For example: "assumequality: 1080p webdl 10bit truehd" and a release flagged 720p h264 is output with "720p webdl h264 truehd"

Should also handle the addition of more quality components as mentioned in https://github.com/Flexget/Flexget/pull/104#issuecomment-29127271
Switched to creating new quality properly