Issue Title: Replace tiles
Description: As is if you say put something on the wrong layer or want to change all of one tile to something else, you have to manually click them all to replace them.
Suggestion: Added option to the fill tool to 'replace all' of one tile with another. So you can change all, or erase all by one tile.
Example: Made a cave, and I want to change the bottom of the cave walls with the version with no floor attach. Select tile with no floor, select to replace all.. click tile I want replaced, changed it through out the map.
Issue Title: Find those tiles
Description: If you some how place a blank tile that is not tile 0, it can lead to passable issues when playing if it's set to X or such.
Suggestion: Could turn off transparency on the tile set so you can see on the map where stray tiles could be so you can remove them, rather then playing 'hide and seek' with them and cycling though the layers.
Be useful for those who are making/editing tilesets and shifting things around, where once there was an object now it's blank, adding it to the map.. now the hunts on for all those blank tiles.
Issue Title: Tile Select
Description: Right now if you want to place more then one tile, you have to click and drag to select the group of tiles to place, but what if the ones you want are not side by side?
Suggestion: Shift click to select additional tiles then on paste, they are placed as a group based on where they were on the tile set, a.k.a as if no tiles were between them on the set
Example: (cave again!) I want to use the two corner walls for the cave, select one, hold shift, select the other, it then places them on map side by side. rather then select one corner, place, select next corner, place.
Issue Title: Check tileset passibility on map.
Description: If you have an error on your passibility on your tile set, or have a tile on another layer that should be passable/non passable yet isn't acting as such... there's no way to really see it on the map.
Suggestion: Simple button to show the passibility of the top most tiles on the map for quick review to be sure 'yes I can not walk past this area' or 'yes this path is clear' etc, Would be useful for quick checking and debugging rather then searching every edge of your map for 'holes' that a player could slip into or such.
Seen a few demos with just such an issue, where someone failed to place tiles/objects that block the player from reaching back into an area they shouldn't have gone to, or didn't realize they mislabled a tile and now it's not acting as it should.
That is all I can think of right now.