fix(windows): improve cross-process refresh

Two changes here:

1. Only post the refresh message to the master controller, so that we
   get a single refresh regardless of how many controllers are
   registered.

2. When Keyman is restarted, the global RefreshTag is reset to 0, so we
   need to do a `!=` comparison rather than a `<` comparison to ensure
   that apps with an existing keyman32.dll/keyman64.dll in memory get
   refresh notifications (as their local `RefreshTag_Process` will
   likely already be greater than `0`).

Also a small additional debug statement.