Adding fixtures dynamically.

- Changed home screen to show a list of fixtures, not a grid.  Maybe-temporary experiment; I think it’ll make it easier to see the fixture names, and maybe easier to assign them to groups.

- Only show stuff on the home screen if there are actually any allocated fixtures.  I.e., we’re showing real data.  -ish.

- Not yet saving that data anywhere.  Also not yet showing the real color-changer for each type of fixture; I’m just getting the fixtures on-screen at all.