Fix droidplanner issue #675: updated the flight mode spinner bar so that its view is updated only after confirmation of the mode change by the drone.
Code cleanup.
Update README.md

Added play store download button and beta info, and cleaned up developer info.
Merge pull request #687 from tensafefrogs/master

Update README.md
Merge pull request #686 from ne0fhyk/fix_issue_675

Fix incorrect Mode Button behavior #675
UI: Change the way the UI responds to a wrongly made polygon.
Editor: Don't raise an exception when trying to modify an invalid survey mission.
Merge pull request #688 from arthurbenemann/survey_ui_fix

Survey UI fix
Version: Releasing version 2.2.4
UX: Fixing User messages to improve User eXperience.
Merge pull request #691 from arthurbenemann/UX_minnor_fix

UX: Fixing User messages to improve User eXperience.