Integrate search.imagej.net features into this wiki's search

[ctrueden]

We can get rid of search.imagej.net in favor of a unified, as-you-type search that covers all the resources. We could also look at integrating the gitter indexer that was running before at CSBD. Integrating search of GitHub resources would be more difficult, but we could use some simple heuristics to at least index files out of repos, perhaps.

[imagesc-bot]

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

https://forum.image.sc/t/content-of-imagej-net-vs-imagej-nih-gov/59920/2