Merge pull request #17 from FreekDB/master

Several refactor actions and solutions for some Checkstyle issues
ViewerFrame:
- Corrected error in createOrUpdateSortPanel: both metric name and metric key are used by createSortOptionPanel now. Pravin: thanks for noticing this!
- Replaced selectedMetricsKeys and selectedMetricsNames with map selectedMetrics.

ChooseMetricsForm:
- Changed two parameter types from List to Collection.
- Replaced a tab with four spaces.