Strata improvement and fixes

[cschreib]

Multiple fixes:

• Fixed edit_box missing the key repeat events.
• Added the OnMouseMove frame event.
• Added missing enableMouseMove and enableMouseClick in layout files.
• Fixed propagation of frame_strata when inheriting strata from parent.
• Removed frame_strata::parent; now the frame's strata is an std::optional, and nullopt means "inherit from parent"
• Switched frame_renderer to use a single sorted vector instead of nested maps(!).
• Fixed OnSizeChanged triggering only inside frame::update() rather than immediately
• Fixed Lua parsing errors not reported