cleanup and renaming of import/export procs in lang::catalog namespace. Now there are really only two public procs to know about: lang::catalog::import and lang::catalog::export. Updating all invocations of the procs and test cases. Adding proc lang::message::unregister for deleting message keys - used in test case teardown.
To speed up package installation we made en_US be the only enabled locale by default. Changed catalog loading to only load files for enabled locales. Added a link in UI so that catalog files can be loaded for a certain enabled locale after installation
