Started working on own graph library.
Added speed graph
Small refactoring of the chart view. Added README and improved GPXManager to have speed data from imported tracks.
Added base implementation for y axis labels.
Added label for graph
Improved activity list
Fixed bug that only first track was displayed in detail view.
Adding public interface to style graphs
Small improvement in Graph view to not show -1 values.
Fixed bug that prevents the activity list from crashing when deleting an activity.