added features
- allow user to define avgSize and UnitCost to mapping scheme
  - updated classes Statistics and StatisticNode
  - new dialog for user input
  - new ms_leaves_table class to display leaves
  - updated exposure generation code
- create exposure from population grids
  - updated data input widget and wizard widget
  - updated project
  - updated preview

updates
- make Fraction to be default sampling option
- updated MSTestCase and TaxonomyTestCase
- save/restore geometry of dlg_size_input, dlg_mod_input, dlg_result using QSettings

fixed issues
- correct algorithm in helper/ms_tree for matching node
- bugs in exposure generation code
- bugs in Monte-carlo sampling

generic
- added GEM logo to main window (with changes in resizeEvent handler)