updates
- allow disable parsing modifier
  - mod tab in main window is removed.
  - node use whole string instead of partial levels
  - but does not have appropriate editing UI. can only edit as textbox
- adjusted logic in MapCanvas refresh in Preview
  now number of refresh is reduced, project loads faster
- fixed error in Statistics.get_samples with method RandomWalk
- created test cases for Statistics.get_samples

generic
- fixed error in gemdb.db
- reduced height of wdg_data to accomodate lower resolution screens