CB-6491 add CONTRIBUTING.md
Split out cordova-lib: move cordova-plugman files

HISTORY:
git log <file> will show no history from before this commit for files that
moved. To see full history use either
git log --follow <file>
or
git log plugman_pre_lib <old file name>

'plugman_pre_lib' is a tag for the last commit made in cordova-plugman repo before
cordova-lib was split out.
Remove all cordova-lib files
Update plugman cli to use cordova-lib
Added cordova-lib to package.json as dep

Forgot to add it before.