Proposed fix for issue #31
General source cleanup: Imports organized, Generics applied.
Fix build warnings and errors about Javadoc, added some comments to the
date constraints.
Merge pull request #32 from bratkartoffel/issue31

Proposed fix for issue #31
Changed fix slightly.
Merge remote-tracking branch 'bratkartoffel/srcCleanup'

Conflicts:
	src/main/java/org/jdatepicker/impl/JDatePickerImpl.java
Replaced all tabs with 4 whitespaces.