fixed issue #4028: Creating multiple MP2-Client instances per machine leads to issues
moved SHOW_MP2_SERVICEMONITOR_MESSAGE to SingleInstanceHelper as well to be consistent with MP2-Client added copyright header removed unneeded usings
added test for ContextMenuCommand
FrameworkElement has a ContextMenuCommand which should execute when the "Apps" Button (next to right STRG) is pressed current implementation was missing the copy of the command when the xaml is read, so it was never available