Fix texture skewing and texture repeats

Closes #4 and #7

Cherry picks 2bbb2aaf30806986c77f45796a7e189efc0f5b2a, fixing the effects of "Slope Skew" and "No Midtexture Skew"/midtexture skewing in visual mode. Visual mode midtexture selection works as expected.

Also fixes texture repeats, displaying them in visual mode. Selection also works as expected.