Fix broken addon browser.

Download to a valid location.  Stop silently failing, show errors to used.

Change-Id: If28e35e2e3dd7f31dd3099349ec8400095edb9af
Fixes-Issue: CLIENT-393
Reviewed-on: http://gerrit.dmdirc.com/2615
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>
Validate swing inputfield on key release.

Change-Id: Ia88fef7d7973df1fd55606b396e0f5955581c129
Fixes-Issue: CLIENT-385
Reviewed-on: http://gerrit.dmdirc.com/2614
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>