Add new update channels for local and CDN testing (#128)

This PR will fix issue #128. @bhearsum can you please have a look at it for feedback? As it looks like we still have to keep betatest for the 31.0ESR branch, and releasetest (until when?).

Also I moved up this block so we do not forget to also update the data for new releases. We also need a CSS fix to make the filter box wider, so there is no wrap for the update channel list.