EDDN: schema - ApproachSettlement

[Athanasius]

Ref: https://github.com/EDCD/EDDN/blob/beta/schemas/approachsettlement-README.md

Currently available on the EDDN Beta service.

[Athanasius]

NB: This was worked on in #1452 BUT I've realised some of that was misguided, or at the very least monitor.py needs reviewing to ensure that both monitor.system and monitor.state['StarSystem'] definitely stay synchronized.

I think it's possible that they'll be incidentally synchronized versus the actual use, i.e. after monitor.system is reset to None the other won't be used until monitor.system once more has a value. But let's be sure.

Also, when working on #1452 it took me far too long to remember/realise that Plugin journal_entry() gets passed monitor.system as its system parameter. So it's valid to think that adding monitor.state['StarSystem'] isn't even necessary. HOWEVER, I think I'd be in favour of just moving all use of monitor.system into monitor.state['StarSystem'] instead. To be honest, all of monitor.py could do with reviewing and having most, if not all, such tracking in the monitor.state dictionary.

Also, with respect to #1228 , other than the backwards compatibility layer, I absolutel think we should not explicitly pass system(_name) into the plugin call point when we have (monitor.)state being passed in, and that can contain (near) everything necessary. Heck, I'm not even sure it needs cmdr(_name) or is_beta passing in!

[Athanasius]

To have this addressed ASAP for 5.3.0 I'll be submitting a PR that simply reverts the monitor.py addition of state['StarSystem']. It's already not actually used by anything (core plugins or other code).

Shuffling things into monitor.state (for availbility) is more of a #1206 thing, so also not for 5.3.0.

And obviously #1228 is its own thing.

So, after next little merge this can be closed for 5.3.0 release.

[Athanasius]

Released in 5.3.0-beta11