Performance improvements

[elliotnash]

Current performance issues:

• Drawing large polylines is expensive in non native map interfaces, even with polyline culling and simplification.

• Calling setState of the sliding modal triggers rebuild of (expensive) elevation graph reducing modal swipe performance

Using native platform maps fixes most performance issues, however, it brings two problems:

• Widget info popups are restricted to just text with an old UI without using a somewhat hacky way to render widgets to bitmaps and set them as a marker icon, which comes with its own performance issues, especially if widgets are not static

[elliotnash]

Gpx files are now processed server side and sent to the client using a custom encoding which reduces file size by roughly 10x, speeding up load time