Improve info messages during RPM creation

* Add `info` message when RPM signing is enabled
* Print ‘creation’ message right before package creation
Switch to OpenSSL::Digest which is threadsafe on 2.1.2

This fixes the following error:

  Digest::Base cannot be directly inherited in Ruby (RuntimeError)

Fixes #334
Make PKG packager aware of scripts with default Omnibus naming
Make RPM packager aware of scripts with default Omnibus naming
Re-add `Project#package_name`

This commit effectively reverts e1172ef864757d6544d4a53cbaa024b3ba5b7afd.

There are many situations where it would be desirable for project and
the generated package name to differ.
Treat `Makeself` package scripts like all others