0.17.4 - Import PPU dumps and more

This version focuses on filing down rough edges and corner cases for the Find, Remove and Sort actions.
If you have used them quite a bit before, chances are you won't notice much difference, but users new to these actions should have an easier time simply using them without running into any caveats.

Some new features include the "invert tile selection" action (ctrl+i), and the "import PPU memory dump" dialogue. 
The latter takes a dumped PPU RAM binary from an NES emulator and opens it as a NEXXT session; complete with subpalettes, patterns, and a 2 by 2 screen canvas. Both "typical" raw memory dumps, and the somewhat size-reduced .ppumem files from Nintendulator, are supported.

The Brush mask editor is a bit easier to use, and there has been some more items and states included in what's undoable/checkpointable.