Track and route editing

Added button to remove all routes from the selected set, indicated by a nuclear mushroom cloud icon.

Added button to heal track, removing a "cut". This replaces 3 connected tracks with a single track.

Fixed bug where deleting a route from an unset signal didn't populate all the other routes at that signal like it should have. This was a regression from how it worked before.

Fixed bug with track highlighting going past one way signals that face the wrong direction. Calculate and store route highlighting on a per segment basis instead of per track.

Made route highlighting calculations use a bitmask for a bit better efficiency.

Made route destinations always show, even when the source signal isn't selected, but in a more muted color. I made the selection color bright white to compensate to be more visible.

Better sanitization of strings to have a filename-safe encoding. I now allow spaces and other weird characters in player names and files. I also fixed a silent failure to save files with invalid characters. Also, I use this sanitization server-side now, which should close some security holes.

Made 'Escape', or whatever the hotkey is bound to, close save/load menus.

Made depot colors actually be random, and avoid reusing color combos as best as possible. Also made the color selection buttons in the depot dialog make it more clear which colors are actually selected for the route.

Draw small numbers over cars so that you know the length of the train and locations of cars, which may be useful for mixed cargo trains.

Fixed some minor UI scale issues: Incorrect window hit detection. Incorrect option checkbox shown.

Added translations of key binding descriptions.