Use P1 inverted color to mark selected bar in editor

[DeinAlptraum]

Before, the selected bar would use P2's color to mark the selected bar. This leads to no marking at all when no color has been selected for P2.

The color attribute for each bar currently holds only a single integer for the player number, since this reuses the coloring-mechanism of the actual sing mode. I chose to mark the selected syllable as belonging to player 99 (instead of player 2) and then making a distinction for that number. The choice is arbitrary, I just didn't want to use 0 since it seems to be already used for something else.

Currently, the color used for marking is the inversion of P1's color. We could also change this to not be based on the player colors at all, and instead use two fixed colors for selected/not selecte or similar.

[barbeque-squared]

I'm fine with hardcoding/(ab)using 99 to be this color (otherwise it's probably going to explode in PR size) however I would request the following changes:

• define a constant eg INVERTED_1 = 99 in UDraw (use a better name if you have one)
• Use that constant instead of hardcoding 99 in UDraw and UScreenEditSub

makes things more self-explanatory when someone looks at this code in a year's time or so.

[DeinAlptraum]

That's a good idea, changed

[barbeque-squared]

Took me a while to realize that 870.patch is not the same as 870.diff. Which makes sense I guess.
And the duet stuff is now also consistent, very nice, thanks!

I've opened #873 to keep track of the whitespace.