v1.5.1

Changes:

• Improved screen redrawing speed (especially when many landmarks are visible)
• UI fixes:
  • Get landmark position before querying its name (PR #33)
  • Do not hide softkeys at orientation changing (PR #34)
  • Update view after crating/renaming/deleting landmark (PR #37)
  • Hold center coordinate unchanged on view size change (PR #38)