FileFunctions: remove unused getJar method

This method is potentially dangerous and duplicates some of the logic
and ideas of SciJava Common's ClassUtils utility class. So if this
functionality is needed in the future, let's use that.
WatchEventsFrame: eliminate usage of Class.forName

Instead, we use SciJava Common's ClassUtils.loadClass method, which is
intended to "do the right thing" (which in this case means using the
current thread's context class loader, rather than the system one).
Merge branch 'class-loaders'

This branch fixes a couple of minor class loading issues.

Specifically, it removes some usages of Class.forName in favor of other
solutions.