#879 Deselecting filters

[Chris Graham]

If you untick all the filter folders and save, it'll appear to go through fine, but doesn't save. This is specifically when unticking ALL the filter folders - you can untick incomplete subsets just fine.
Now I understand you do actually have to have at least one filter folder, but the UI should give some feedback when you try and do something invalid.

On a similar note, if the unsure folder is set to blank, the UI happily let's you keep that - but actually running a scan will error out. Perhaps some kind of UI feedback (e.g. JS validation) could indicate this so you can fix it early on. Not a biggie.