getInstalledVersions: skip legacy entries

When we switched the checksumming to skipping certain parts of the
pom.xml and the manifest, we needed a way to represent different
checksums for the same file. These checksums were stored in the cached
checksums for speed.

However, almost two years after that switch, this information is no
longer useful for Fiji's bug submitter (for which we invented this
method).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
getInstalledVersions: list only an abridged version of the installed files

Instead of a long, long list of files (most of which are likely to be
up-to-date, anyway), let's just list the files which are not up-to-date.

This requires the list of active update sites, of course, because
otherwise one would not know *which* file versions are to be considered
up-to-date... ;-)

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
getInstalledVersions: also list the file status

While we're already switching to showing only the files that are not
up-to-date, we might just as well provide the information about the
file status (which is fully well known to the updater).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'bug-submitter'

The changes in this topic branch are primarily intended for the benefit
of Fiji's Bug Submitter (which asks the Updater for the file versions to
be submitted together with bug reports). The net result is a much more
concise version of the list of local files.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>