Register FITS MimeType for KStars. This enables KStars to open multiple FITS...

Register FITS MimeType for KStars. This enables KStars to open multiple FITS files. However, KStars creates a new instance and does not re-use the instance thus far, so every time the user selects KStars to open a FITS file, a new KStars instance is started
We could use DBus to find existing instances since the openFITS function is available via DBus so this needs more work to be more friendly.