Mypy runner script

Introduce a mypy runner script that runs mypy, so that every developerwill use mypy consistently. Here are some things you may want to do inthe script:

• Ensure that the correct version of mypy is installed.
• Specify mypy config file or command-line options.
• Provide set of files to type check. You may want to implementinclusion and exclusion filters for full control of the filelist.