[STF] extended context menu API

As extension for the superbot this is an implementation of the runAs
context menu in the package explorer view.

Right now there is only the run as "Java Application" context menu
implemented.

Change-Id: Ia7f97d57e146faa6667fc7d7844cc07c09a49302
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1058
Tested-by: Jenkins CI
Reviewed-by: Bernd Bieber <brotlee@zedat.fu-berlin.de>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>