CLI: Support -g for widgets

[FokkeZB]

• Determine a global path to use and make it configurable
• Install widgets per version like Titanium modules are
• Create a symlink in the project to point to it.

Credits to Bert, Appcelerator ;)

[grantges]

also a way to alter the configuration of gittio so that you can specify the global install directory

[FokkeZB]

@grantges covered by #62