Add URI widget

[tischi]

Hi @imagejan et al.,

A challenge is that we would like to prepend the file: scheme for local paths. However, there were issues with making this work properly with the persists option. @imagejan can explain this better.

If we cannot find a good solution for automatically prepending the "file:", maybe we could also consider just not doing it.

It is important that down-stream code can deal with the URI. I wrote here some code to see whether one could live without the "file:" and it seems to be possible. Basically, the pattern would be that one defaults to "file:" whenever one cannot identify the scheme. Maybe that is fair?

[imagesc-bot]

This pull request has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/fiji-friends-weekly-dev-update-thread/103718/8

[tischi]

ping @bogovicj ☝️