The default license created with rebar3 templates is a BSD 3 clause
license. However the .app.src file generated do not include the license
there.
This adds the license type, fixing #1447.
The first variable can be unkeyed and the provider will sub in the
variable name 'name'. Additionally, the built-in templates and
documentation have been updated so that 'appid' is now 'name' and the
alternative commands are shown.