Add simple initialization based configuration support and the ability to configure if the sign in is stored in the session

[krsyoung]

This PR includes a feature that @gonzalo-bulnes has identified in issue #19 (and could possibly help with #20 and #12).

1. Initial configuration framework to support an initializer based configuration file
2. A single configuration to define if the token authentication should be stored in the session (i.e. can the user navigate to other pages as an authenticated user after a single token authentication).

I have included updates to the documentation however no test cases :(

@gonzalo-bulnes please let me know if it helps if I break these up more cleanly between issues #19 and #20. Thanks!

[gonzalo-bulnes]

Hi @krsyoung! I cherry-picked your code from #32 in order to take advantage of the @joel improvements (see #23) and, since the branch is merged I'll close both PR.

Many thanks to both of you for this configuration framework!

@krsyoung Since you asked about the RSpec test cases: I've deeply refactored the Cucumber "dummy apps generation framework" and I believe it became a lot more readable. Take a look at the doc/features.html file to see how the RSpec use cases are build : )