Implementation of Planning/Measurement plugin consistent with latest project structure.

This is a modified version of the Planning/Measurement plugin that:
1. Is independent of OsmandSettings.
2. Is a self-contained plugin that can be installed using the supplied PlanningPluginActivity
3. Is the fully implemented version of planning and measurement submitted for inclusion in early 2012. It has been updated to the latest plugin format and fully integrates into the base menu structures. It should be used to replace the current Calculate Distance plugin, which was a partial implementation of the original proposal using the plugin format.
The original implementation was operationally tested as a GPS and planning tool for 2 months during a motoring holiday through several European countries and the new features were found to be extremely valuable, particularly the display zoom and planning-track save/reload.