Made the default GPG config file overridable

[angelos-p]

Allowed the user to be able to choose a different default GPG config file during key creation while keeping the current one as default.

In order to do this, I created a method called configure_config_file that takes the args and the gpghome directory and creates the config file by copying the default gpg config file which can be either the default one in /usr/share/gnupg/gpg-conf.skel or a user selected one to a new file and appending the GLEP:63 requirements in it.

That way the user can decide which GPG key configuration to use while still keeping the mandatory GLEP:63 requirements.