Make a muscle_manager executable

[LourensVeen]

MUSCLE 3 users will have to run the manager, in addition to their own kernels. To make that possible, we'll need a muscle_manager executable that does so. The goal is for the user to be able to run the manager using

$ virtualenv /path/to/env
$ source /path/to/env/bin/activate
$ pip install .
$ muscle_manager

The Click library is a nice way of making command line tools. See http://click.pocoo.org/ and https://kushaldas.in/posts/building-command-line-tools-in-python-with-click.html. The code for the entry point should be in muscle_manager/muscle_manager.py. We don't need command line parameters initially, but they will come (e.g. log file location, log level, yMML file, etc.).

[LourensVeen]

Initial version in c0730d2c5fe19d45eea9be95bb5a1d4840e6508e