Fix some space inconsistencies, force relayouting on resize.

REVIEW: 110226
Note: Review request consists of the following commits:
beb86d0 Fix some space inconsistencies, force relayouting on resize.
3046305 Restrict maximum size of shown text.
7daf920 Strip summary and author tags with excessive size.
3088eeb Equal button width. Show disabled update button for !upgradadable ones
5455fdb Migrate newstuff config file to MarbleDirs, use new internal dialog.
aef3e29 Finish display and actions.
36eb204 Publish download progress as model item property
600e127 Fix querying payload size (needs to follow redirects)
4fc11ba Finish display, actions, progress report.
e0df23b Replace browser action with an in-app installation dialog (in progress)
3f8cfe0 Download preview icon and use as decoration
8c60cbc Rename members to indicate they're URLs, not data