Add "Convert single-channel to multi-channel image" tool

[kostrykin]

…add some other minor updates for improved clarity.

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[bgruening]

Is numpy interesting for the users.

[kostrykin]

Not sure, this tool is a very thin wrapper around numpy.dstack, and, regarding what we agreed as a community, this seems to be an edge case:

If a Galaxy tool is a thin tool wrapper (e.g, part of a major tool suite), then the name of the wrapped tool (and only the name of the wrapped tool, subsequent to the term “with” as in “with Bioformats”) should be used as the description of the tool […] The tool description should be empty if a tool is either not part of a major tool suite, or the main functionality of the tool is implemented in the wrapper.

One could argue that NumPy is a tool suite… But I see your point. However, there already are a few other tools "with NumPy". I'd be open to treat libraries as an exception here, as they are rather libraries than tool suites, but then it should be removed from all tools all together.