Vector Tile support
This is a WIP port for the upcoming Mapillary v4 API.
Major changes:
* The different download methods are no longer supported.
* No uploads to Mapillary are possible (v4 upload API is currently
unknown)
* Currently requires a patched version of JOSM (see JOSM #17177)
The only tested items are as follows, use anything else at your own risk
(but if you do, please let me know if it worked):
* Image download and viewing
* Moving forward/backward in a sequence
* Image detections for point objects ("instances"), traffic signs, and
segmentations can be shown in the image viewer. Segmentations are
disabled by default (set the advanced preference
`mapillary.image.detections.segmentation` to `true` if you need
segmentations, expect slow download speeds)
* Changing sequences
* Downloading point object layers (note: Smart Add does NOT currently
work)