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