Yeoman generator checks don't actually check installed version

[sstone1]

npm view generator-fabric version checks npmjs.org to see if the specified package exists, and then returns the latest version of that package. It does not actually check to see if the specified package is installed locally, or if it's the right version - and we need to do both!

npm ls -g --depth=0 generator-fabric will check to see if the specified package is installed locally. We also need to check if it's of a version that is compatible with the extension, e.g. the work in issue #51 will require generator-fabric@0.0.4 or greater to be installed. We will need to prompt the user that they must upgrade their installed version if this is the case.

[sstone1]

Duplicate of #32.