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
Restore if minimized and set to ActiveForm when message from another instance received (to set focus and bring it to front)
write message to console and exit environment if another instance is running improved comments and moved message posting to SingleInstanceHelper
moved SingleInstanceHelper from MediaPortal.Utilities to MediaPortal.Common