This commit makes a few changes:
* Uses "%mamba" over "!mamba" - has support for micromamba
* Adds "-c conda-forge" - I found this necessary, at least for
  micromamba
* Adds prefix delimiter manipulation to account for Windows paths

This commit fixes how we set the JAVA_HOME variable for PyImageJ in the
dynamic install cell. The problem was 2 fold. (1) We were missing a
leading slash and (2) did not have platform specific JVM library
locations.

We may need an additional one for macOS -- this needs further testing.