bridge: Hold refs on CockpitPackage while we add/replace

While adding and replacing packages with aliases, and putting
checksums in place, hold references to the packages themselves
so that if their main name gets replaced during processing,
we don't access invalid memory.

Closes #1372
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
tools: Simpler jslint when not processing HTML files

When processing HTML files our jslint invocation has to be rather
complex and hokey. But for javascript files, it can be pretty
simple.

Closes #1373
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>