DataEntryForm: refactored displayNoReportsFoundDialogue method; other small changes

DataEntryForm:
- Added TODO: pass rootDirectoryName as a parameter to displayInitialDialog.
- Added TODO: can we use JOptionPane.showConfirmDialog(null, message, "title", JOptionPane.YES_NO_OPTION)?
- Refactored the displayNoReportsFoundDialogue method to fix several Checkstyle issues and to improve naming & readability.
- Removed unused fields parentMain, parentViewerFrame and appProperties. Also removed the related constructor parameters.
- Set the frame title to "Date Filter" in the displayDateFilterEntryForm method.
- Moved two Dimension constants to the Constants interface.
- Created ERROR_TITLE constant.
- Used Constants.CANCEL_BUTTON_TEXT.
- Some other fixes of minor Checkstyle issues.

ViewerFrame:
- Added TODO: the menu stops working after setting the date filter; resizing the application makes it work again?
- Used "Set Date Filter..." instead of "Set Filter..." for report date filter menu item.
- Moved three Dimension constants to the Constants interface.
- Removed unused field appProperties. Also removed the related constructor parameter.
- Removed parameters for calls to constructor of DataEntryForm.

Main:
- Removed parameters for calls to constructors of DataEntryForm and ViewerFrame.
- Replaced ArrayList by List where possible.

ChooseMetricsForm:
- Moved a Dimension constant to the Constants interface.
- Used Constants.CANCEL_BUTTON_TEXT.

DetailsFrame:
- Moved a Dimension constant to the Constants interface.

Constants:
- Added DIMENSION_5X0 constant and removed unused DIMENSION_0X5 constant.
- Minor textual changes to comments.