In game GUI refresh to focus on user

Update and replace the in-game GUI with new popup aids/windows with the following aims:

- Familiarity: MSTS users should feel reasonably at home.
- Ease of use: Less experienced users should be able to get and keep moving easily.
- Challenging: More experienced users should be able to make it sufficiently hard to get and keep moving.

General ideas for the windows:

- Appropriate aids to get started should appear by default.
- Aids will have different "levels" to show more or less detailed or complex information based on user skill.
- The visual display should be unobtrusive and aids should get out of your way when possible.
- Not all aids will be appropriate for all users or all activities.
- Every aid and aid state will be changeable in-game.
- Position, visibility and state for each aid will be saved and restored.

Possible windows include:

- Help
- Locomotive
- Route
- Activity (including for timetables)
- Operations

For example, the route aid window (AKA track monitor) could be something like this:

- Beginner - stylized graphical view of upcoming track indicating speed limits, signals and points-of-interest (stations, sidings, reversing point, etc.). The view will support both horizontal and vertical orientations, moving up (vertical) and right (horizontal), using symbols for all the key upcoming items and text labels for key distances, speed limits and station/siding names. It will also be resizable in the direction of the graphical view, up to the length of that display dimension. The display will be adjusted for the train's speed, showing at least 5 minutes down the line.
- Intermediate - text showing current speed limit, next speed limit with distance, next signal with distance, next point-of-interest with distance, current gradient and next gradient with distance.
- Advanced - text showing next point-of-interest and current gradient.

This is still very much in the drafting state :)