Add support for trip layers

[tjukanovt]

Expected behaviour
I would like to export normal vector data formats from QGIS with timestamps as trip layers

Current behaviour
Currently the trip layer in Unfolded Studio is a specific LineString GeoJSON type.. This is not really widely supported, so producing this requires custom code.

Describe alternatives you've considered
The plugin could have a functionality or a separate dialog, where the user could indicate the timestamp column (and possibly altitude). Latitude and longitude could be identified directly from the data. To keep things simple, the plugin could require the data to contain valid timestamps (in a datetime format or epoch).

This sort of "standard" tabular movement data could work as a first test case: https://github.com/tjukanovt/tjukanovt.github.io/blob/master/data2share/trainGPS.csv