Merge pull request #12 from wardies/master

Add min distance preference and donut filter, plus minor refactoring
added analytics xml and updated database with heights
added heights
fixed bug where heights weren't showing
Fix #13 by simplifying `filteredDirection.getDirection()` to return the sum of directions modulo 360 degrees.
Fix #14 by encoding degree symbol in a string.
fixed averaging bug (preferences not being read properly. Imported British Hills data