WL-3184 Create a local simple-signup-entityprovider

The simple-signup-entityprovider cannot producer calendar events with the
new version of signup that we are running locally because it doesn't assign
any meeting coordinators. This defines a local version that we can play with
Merge pull request #30 from ox-it/WL-3184

WL-3184 Create a local simple-signup-entityprovider