avoid dependency version conflicts with other htmlwidgets

There has been some discussion about this here #143

In short, if two htmlwidgets are being displayed on the same page and they use the same Javascript dependency but different versions, those dependencies can overwrite each other when they are loaded/added to window. Additionally, if they have the same name in their YAML file, htmlwidgets will only load the one with the highest version number. I point this out separately because even if htmlwidgets did load both versions, there could still be a collision when they were loaded onto window. This is most notably an issue with incompatibilities between D3v3 and D3v4.

It would be great to collect all discussion, ideas, links, hints, etc. about this problem in one issue here. @timelyportfolio, you seem to have been following this problem for a while, so it would be nice if you could copy in here those ideas and links to similar solutions or discussions in other packages.