CB-7100: Use npm based lazy-load by default

Older git based download is still available under a --usegit flag e.g:
`cordova platform add ios --usegit`
`cordova prepare ios`

The cached files are stored in different locations depending on where they
were downloaded from because we don't want dirs that are not npm packages in
an npm managed cache dir.
~/.cordova/lib
~/.cordova/lib/npm_cache

If a copy downloaded via git already exists in the cache, lazy_load should
not attempt to download another copy from npm.