Devise strategy - bring back old method of configuration

In this commit - https://github.com/adamniedzielski/simple_token_authentication/commit/f72f6e54237263ba92e97e6f1386f99fbe41f2c8 @jbender changed the way how simple_token_authentication can be configured. I think that the previous way was better, because it lets you do config on ```SimpleTokenAuthentication``` module instead of ```Devise``` module. 

This encourages gem users to create separate initializer with configuration related to SimpleTokenAuthentication. In my opinion this is good - there are already many configuration options in ```Devise``` module, so having separate configuration specific only to SimpleTokenAuthentication is good.

What do you think?