Current Trip add instruments id and then export to Therion .th

[CaverBruce]

Would be nice if ST could provide a current trip input fields to record the 'book' id and instruments id(s)

	instrument  notes "Nomad Spectra"
	instrument  instruments "distoX2 2973"

These should be exported to Therion format and ptopo-txt format as well. See also #98

[CaverBruce]

I also noticed that 'current trip' data does not persist when a new file is created. Often one survey trip follows another, with the same team, similar roles and similar comments to be entered. I would prefer that the 'current trip' data entered persists, probably as that most recently entered (for any file - like PocketTopo) or possibly as that of the most recently opened file prior to th ecreation of the new file.