Allow users to set package name aliases

[tir38]

Similar to #40 but for package names. Something like this

$ ax package_alias myapp com.example.longpackage.myapp
$ ax package_alias other com.example.some.other.package
$ ax package_alias

  myapp -> com.example.longpackage.myapp
  other  -> com.example.some.other.package

$ ax version_name myapp

1.3.0

This remove having to type in and remember package names. This will also cut down on typos. It might be easier to do tab completion on aliases, instead of all packages.