Implement 'View' drop-down menu.

[waptaff]

Allow viewing the map at the same location on external map providers (Google, Bing, others are easy to add), using a new 'View' drop-down menu.

Note that the map type (tiled roadmap / satellite) for Google Maps is not working properly despite the URLs following the official documentation, this is a known problem:
https://www.reddit.com/r/GoogleMaps/comments/1f9y465/how_to_force_a_map_type_roadsatellite_in_a/

Official documentation is at:
https://developers.google.com/maps/documentation/urls/get-started

Obviously this patch is a first draft and main project maintainers should feel free to rework this so it suits them.

Might close issue #108.

[deevroman]

Hi, thanks for the PR. I don't fully understand the final form of #108 yet, but I'm considering it as one of the options. I especially like that it's easy to access on mobile devices.

A couple of comments on the layout:

It is worth noting that we can try to somehow post a place horizontally (show the first few links?)

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In the general features, I would like from #108 of the next:

1. The ability to add your own links (but the UX of link parsing is unclear)
2. Import a list of links from OpenSwitchMap (again, OpenSwitchMap has a bad UX showing many links at once)
3. Work on Firefox for Android. OpenSwitchMap/OSM Smart Menu poorly adapted.
4. It seems that the blue button is now quite intrusive to enable it by default. But I still have no idea how to do it better. (it can be added to the right pane of the map, but I'm not sure that this is convenient)

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Probably several weeks will pass until the next update, so you can calmly experiment. I will warn if I start working on this function.

[waptaff]

Pardon my ignorance — I didn't know about OpenSwitchMaps and honestly it fills my need, as I don't need map switching on mobile.

Alas that means I won't be working on this patch anymore — feel free to keep it as inspiration, to improve on it or to reject it.

Despite this, for sure I'll keep running the main userscript, there are a lot of useful tools in it and I like what its future could be, thanks for it.