Remove deprecated run methods

These were put in place before the 2.0.0-beta-7.6 release, so that
downstream code had a clear migration path (despite the fact that
ImageJ2 is still in beta, we try to keep old API in place for one
release as deprecated before removing).

However, in this case, due to method signature ambiguities, it is
important that the deprecated methods be removed ASAP since they
unfortunately interfere with use of the new method signatures.
ScriptService: add method to get scripts directory

This is the directory that ImageJ will scan for scripts.
ScriptFinder: crawl directory given by the service

In this way, the directory to crawl for scripts can be overridden in an
extensible manner.
SystemInformation: wrap long line
Organize imports
Updater: use a slightly more meaningful User-Agent

This will allow us to assess a little bit better what Java/Operating
System combinations users really use, to plan ahead for Java 7.

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