Update TileMainEditor.cs

Added the ability to choose which sorting layer newly added tiles are set to, so it's easy for us to order tiles.
Update TileMain.cs

Added necessary additions here to allow us to choose which sorting layer tiles get added to.
Added ability to add materials

Now you can choose a material to add to the tiles.
Added ability to add materials

Did necessary additions so we can have the ability to choose a material to add to tiles.
Merge pull request #3 from bloeys/patch-1

Feature addition: choosing sorting layer for tiles to be placed on and ability to add materials