Add elevation graph

[lynxize]

Adds a simple elevation graph to the graph tab.

Since having 2 or 3 graphs on the same page can get a little crowded, I put the elevation graph behind a preference that defaults to false. It would probably be better to make the entire graphs tab scrollable to fit, but I'm very new to android stuff and didn't want to make too many changes.

I don't have any workouts with heart rate data so I wasn't able to test how it behaves with all 3 graphs.

Related issues:

• No altitude tracking function #229
• [feature requests] add other info in the graph (target pace, altitude, cadence) davidedelvento/runnerup#25
• Feature request: elevation gain #1167 (not solved)

[gerhardol]

This could be added as a second graph instead, in both hr/pace graphs.

Note that thedependency providing the graphs need to be replaced. It is not compatible with jetifier.
The dep could maybe be fixed too.