Add log endpoint

[kueda]

Add support for POST /v1/log, probably something like

inatjs.log( {
  error_type: "TypeError",
  error_message: "Cannot read property 'prefers_scientific_name_first' of null",
  backtrace: "some\nlong\ntrace"
} );

If you want to get really fancy, it would probably help it accepted a JavaScript Error object and populated the values from that.

Another possible feature would be to support GET /v1/log, though we might need to distinguish error logging from this kind of status logging, like

# Requests GET api.inaturalist.org/v1/log?foo=bar
inatjs.log( { foo: "bar" } )

# Requests POST api.inaturalist.org/v1/log
inatjs.logError( someErrorObject );

Context: I think this would be useful for using our own infrastructure for logging and error reporting from JS client apps. We could certainly use it in our React frontend on the web, but also in the React Native app.