Force version, update pub uploaders

I added a flag --version that in combination with --force allows us to reset the version of all the client libraries on GitHub.
so update.dart --force --version=0 will set all client libraries to version 0.1.0

I also added an (untested) block that will update the uploaders of the pub package. I think this is necessary so both of us can update the package on pub.

@financeCoding can you test if I broke the pub upload somehow that way, thanks.