GridHighlighter test project

GridHighlighter based on XNA.
Creates a two dimensional array of the new class "Tile", which is
filled, then checked for the current mouse position within the Update
functon and then drawed within the Draw function. The Tile below the
cursor is white, all others are black.
It would be more performant to first fill the whole window black and
then only draw the Tile below the cursor white, instead of drawing each
tile individually, even the black ones. But I just assume we're going to
draw them individually eventually as we're filling them with different
textures, so I already draw them one by one.