grid: Add range grid

Add a grid that performs a range search via a SQLite R*Tree virtual
table, for formats that can't use the tilemap grid because they don't
record the row/column of each tile.

Adding tiles to this grid is very slow.  The R*Tree virtual table
performs several operations on its backing tables for every insertion.
Opening Mirax2.2-2.mrxs via the range grid takes over 5 seconds on my
system.  We may want to replace this implementation eventually.