DataEntryForm: refactored displayDateFilterEntryForm and displayRootDirectoryChooser methods; other small changes

DataEntryForm:
- Added TODO: can we use JDialog instead of JFrame (that way we can set the owner to the viewer frame)?
- Added TODO: "extending JDialog is as bad as extending JFrame" see http://stackoverflow.com/questions/15429653/how-to-set-the-jframe-as-a-parent-to-the-jdialog
- Use current values for date filter dialog.
- Refactored the displayDateFilterEntryForm method, splitting off the createDateChooser, createDatePane, createButtonPanel and showErrorMessage methods; fixing several Checkstyle issues and improving naming & readability.
- Refactored the displayRootDirectoryChooser method to fix several Checkstyle issues.
- Created the DATE_LABEL_WIDTH and DATE_LABEL_HEIGHT constants.

Main:
- Added TODO: can we decrease code duplication between the runReportViewer and updateReportViewer methods?
- Fixed several small Checkstyle issues.
- Added the getFromDate and getTillDate methods to enable initialization of the date filter dialog.
- To optimize feedback to the user in the runReportViewer method, call the dataEntryForm.displayInitialDialog method as early as possible and call the dataEntryForm.disposeInitialDialog method as late as possible.
- Changed the parameter type of the updateReportViewer method from Boolean to boolean.

Constants:
- Added DIMENSION_0X5 constant.