Implement semi-automatic -r/--recursive

Commands that only make sense applied recursively (get-deps, etc.) are
automatically applied recursively. Everything else requires explicitly
passing -r/--recursive.

Before:
$ rebar get-deps compile

After:
$ rebar get-deps && rebar -r compile
Make 'compile' recursive by default
Allow extending recursive_cmds list in rebar.config

If local rebar.config has {recursive_cmds, list(atom())}, use it
to extend the list of automatically recursive commands.
Revert "Make 'compile' recursive by default"

This reverts commit 6b0b86c82152944b370df6a42195aa95ced3bf88.

If you need 'compile' to be always applied recursively in a project, you
can do so by adding the following to rebar.config:
{recursive_cmds, [compile]}.
Implement meta command 'prepare-deps'

'rebar prepare-deps' is equivalent to 'rebar -r get-deps compile'.