#74: added closable support
ups, forgotten to add and commit for checkbox
#41: improved test, fixed bugs
#78: added maximize support for popup
further improvements on widgets (Toolbar, ButtonPanel, ButtonGroup,
etc.) and some fixes (module added to pom, endless loop fixed in
combobox)
fixed and improved on general findings
#49: dropped support for java < 1.7
#49: make use of try-with-resources, changed temporary and deprecated
add/getSuppressedException to add/getSuppressed