map tab improvements

[FramePerfection]

• stabilizes the core loop timing, leading to a stable 30 (or whatever is configured) FPS for a less jarring real-time experience
• decouples view modes, adding context menu options to manage multiple views of the same kind (i.e. many of each "Top Down", "Orthogonal", "3D")
• renders tape measure distances in all view modes, and provides toggles to turn individual dimensions on/off
• Enables object hovering on map popouts
• Adds an option to highlight worse than 4/4 quarter-step frames in the "Previous Positions" tracker
• fixes an unrelated crash with 2D Distance computed variables

For the time being, I'll consider this as resolving #55.