FMod - Render copied blocks

Today I tied together all the infrastructural loose ends into a completed implementation of a clipboards palette for Abiathar. A view state - just like the ones for real levels - is maintained for each of the nine copied blocks. The clipboards palette form creates a level wrapper and a view state when a copied block is stored in a slot. The main renderer function now takes a plane filter function, which the clipboards palette uses to hide planes that the copied blocks do not contain. This avoids rendering an opaque background (of the background zero tile) when the copied block doesn't include the background plane. Since the palette form uses the main rendering function, hidden planes are also hidden in the palette. Likewise, tile properties and the find highlight are displayed if appropriate.

To select a clipboard slot for retrieving or storing, the user can click the image, click the label, or press the appropriate numeric key on the keyboard (probably the numeric keypad since the form is laid out to match that, but the normal numbers work too).