Update Common/Source/Geoid.cpp

Added interpolation between values of the EGM96 matrix to get the geoid separation
improved drawing of Glide polar in statistics dialog
Target dialog for AAT sector fixed

Before the change a Target dialog for narrow AAT sector (like 90o - 180o) was
centered at the center of the circle used to draw the sector and zoomed
to view 2x its radius. Because of that sector was really hard to manage in
AAT tasks. Now the same sector is centered on the screen and stretched on full
screen.
Added information about landable waypoint on Task Edit screen

It is really important to be aware during task planning that we are
dealing with landable waypoint. If we miss that for example finish for
AAT task is a landable we can have big problems to complete task safe or in
good time.
Merge branch 'DrawPolar' of http://github.com/brunotl/LK8000 into new
Merge branch 'target_aat_sector' of http://github.com/mpusz/LK8000 into new
Merge branch 'landable_wp_in_task' of http://github.com/mpusz/LK8000 into new
Merge branch 'master' of http://github.com/alus-/LK8000 into new