Add requirements.txt

[ihnorton]

No description provided.

[ihnorton]

@ljod @zhangfanmark this will allow pip to install dependencies. Eventually it should probably also include VTK, but leaving that off for now because of the version questions.

[ihnorton]

(and will allow the SlicerWMA installer to avoid enumerating each dependency)

[ljod]

Is this for use within Slicer or general installation or both? Also, we are currently at an older VTK than Slicer. But I wonder if it is ever safe to install a VTK python package in the python that Slicer uses? Since it is also compiled as part of Slicer itself?

[ihnorton]

Both; it would also help to make a pypi package eventually (not working on that now of course).

I wonder if it is ever safe to install a VTK python package in the python that Slicer uses?

Yeah we need to double-check compatibility with Slicer VTK.