Fix for js/css not being seen by RT::Squish (RT#91227)

RT::Squish can't find the js and css files of RT::Extension::Announce, as per https://rt.cpan.org/Ticket/Display.html?id=91227. This patch fixes that, by moving those files into the static/ dir.

If you upgrade to using Module::Install::RTx >= 0.31, the patch to inc/Module/Install/RTx.pm is unneccesary.

/Lars