Fix trailing slashes in Project Manager

[Bubballoo3]

There are essentially two places where the project manager relies on user-provided paths, during project creation/import, and in the SHARED_PROJECT_PATH environment variable. Both of these values have been expecting no / on the end of the paths, and when a trailing / is passed you get bugs as the paths that are composed from these pieces have // in them. We need to go back and make sure that whenever we take user input, we convert the value to a Pathname and do #join so that ruby handles the slashes.