escape close current dialog and transfer key focus for further keystrokes

JAL-796 and JAL-1662 recognised a problem with Jalview's dialogs that they are not cleared when escape is pressed. This should happen for *all* popup dialogs, allowing the user to step back from any operation they were beginning to perform (but had not actually enacted via an OK or Submit button press), with the caveat that a warning dialog should be shown for operations where valuable input data might be lost (e.g. a cut'n'paste dialog or a configuration dialog box where settings were modified).

When a dialog box is closed, input focus should always transfer to the originating alignment panel, so the user can continue to enter keystrokes as necessary (e.g. CTRL-F to open the find, followed by ESCAPE, followed by CTRL-F again should open another find dialog box for the same alignment).