Install svZeroDSolver via pip

[richterjakob]

Is your feature request related to a problem? Please describe.
Using git submodules can be quite cumbersome and is fom my experience only favorable if the main module and the submodule are developed closely and frequently together. However, that is not the case for the ZeroDSolver. An installation via pip is in that case easier to handle and IMO the better choice for the svZeroDSolver.

Describe the solution you'd like
The svZeroDSolver now supports installation via pip (see here. It can be installed just like other side packages. See #800 for more information on the current procedure for adding new packages to SimVascular's built-in python.

Interested parties
@mrp089

[mrp089]

@ktbolt What changes do I need to make to install svZeroDSolver via pip?

I'd like to finally merge #841 into master and would use this occasion to bump svZeroDSolver to its newest (fastest) version using pip. Thanks!