Layout and description changes; removed the word 'Plinth' from the UI

Created by: fonfon

• added titles to the main menu items (visible in many browsers when hovering the link [w/o js])
• adapted the descriptions of the main section landing pages
• changed the menu item from 'FreedomBox' to 'Applications' because I think it's misleading, and hoping that 'Applications' fits better. We can re-introduce the 'FreedomBox' menu item when we have a 'proper landing page' (thinking about the dashboard).
• removed cfg.product_name (Plinth). I do no think that users should be shown this name, so I removed it and adapted the tests. In every place where it was used, 'FreedomBox' was the more appropriate term instead of 'Plinth'.
• removed the [Name] section and moved cfg.box_name to [Misc], because cfg.box_name was the only item left in there.

Feel free to pick only some of my commits if others are too controversial and should be discussed first.

Looks good. I've rebased and merged these changes.