acts_as_token_authenticatable adds unnecessary methods to ActiveRecord::Base

[philayres]

While working through the PR for #300 I found that adding an override for the attribute authentication_token caused one of my Rails apps to fail. This was reporting ActiveRecord::DangerousAttributeError on the attribute.

After digging around I found that acts_as_token_authenticatable really doesn't do much. The file it is defined in gets applied to ActiveRecord::Base, which meant that all changes made in there become part of that Base class. This led to ActiveRecord noticing that the attribute I was attempting to override was overriding what it considered to be core ActiveRecord functionality.

I have worked up a PR to split out acts_as_token_authenticatable so that the underlying functionality is only applied to the models the method call appears in. This follows the approach I see you already have for the controller handler acts_as_token_authentication_handler.

Unfortunately this PR was worked up based on the work already done for #300. It doesn't make sense in my opinion to go back and rework everything against the current version, so I propose that the PRs for this issue and #300 be adopted together. I hope you are OK with that.

I'll submit the new PR once we've made progress on the first one.