styles related to #id_tray & apparatus separated out into _tray.scss; new tray.js computes the cell size of the tray grid for item organization; room.html now sports the grid as a separate div so as not to interfere w. tray styling or size; new tests in FTs.test_room_tray

src/static_src/scss/core.scss

@@ -6,6 +6,7 @@
 @import 'gameboard';
 @import 'palette-picker';
 @import 'room';
+@import 'tray';
 @import 'billboard';
 @import 'game-kit';
 @import 'wallet-tokens';