Revert "Force a minumum size (800x600), also helps for background resizing"

This reverts commit 55e4d7b91c06b1409cd59ac58c264ac96cd9ef77.

Conflicts:
	src/main.c

https://bugzilla.gnome.org/show_bug.cgi?id=709595

Conflicts:
	src/main.c
Set a size request for the clutter widget

This prevents us from resizing the window to ludicrously small sizes.

Also, no longer set a default window size, since this is no longer
required now that the clutter widget has a size request. GTK+ will pick
a nice window size to fit the tile size.

https://bugzilla.gnome.org/show_bug.cgi?id=709595