Make server-version a required parameter to 'ml new' or 'ml init'

[peterskim12]

I'd like to propose making server-version a required parameter to 'ml new' and 'ml init'. The way that Roxy does bootstrapping didn't change from ML5 to ML6 so users didn't have to set server-version to 6 even if they were using ML6.

However, with ML7 being released soon and a substantial percentage of the user base likely still at ML6 (or even ML5) for a while, it might be a nice usability enhancement to require people to provide a --server-version command line parameter when running 'ml new' or 'ml init', since there is no way for us to query for the ML server version and provide a helpful error if the server-version in the properties file is incorrect.