Some refactor steps and solutions for Checkstyle issues

ViewerFrame:
- Looked into the Checkstyle MagicNumberCheck: it currently only allows the multiplication operator to be used in constant expressions (& also unary plus and minus).
  Workaround for the moment is to use CHECKSTYLE_OFF/ON markers for the MagicNumberCheck in applicable places.
  See the ALLOWED_PATH_TOKENTYPES array in the MagicNumberCheck class:
  [MagicNumberCheck class](http://checkstyle.hg.sourceforge.net/hgweb/checkstyle/checkstyle/file/a485366ec8c3/src/checkstyle/com/puppycrawl/tools/checkstyle/checks/coding/MagicNumberCheck.java)
- Split up the getControlFrame method into smaller parts by creating the createControlPanel, createZoomPanel, createZoomButtonsPanel, createZoomXAxisPanel and fillZoomXAxisPanel methods.
- Created the VIEWER_WIDTH and SPLIT_PANE_1_WIDTH constants for GUI dimensions.
- Removed the null checks for the orderedReportUnits and desktopPane fields because these always refers to an actual object, making the checks unnecessary.
- In the sortChartFrameList method, all deselected reports are collected while adding the selected reports, making it easier to add them after the for loop is finished.