Engine Files - (Serial number plugin architecture)

[Tyler Hall]

Hi, all.

Just want to post an update about the latest commit I pushed this
morning and last week.

I re-factored all of the serial number / license logic into "Engine"
files. Each engine file is a subclass of the abstract Engine class.
This allows you to define (easily) your own generateLicense(),
emailLicense(), etc functions. Prior to this change, Shine was
becoming a soup of if/else statements to deal with the varying license
types. This should help solve that problem. Feel free to email with
questions.

Also, there's some new code in place (license-inapp.php) that supports
the "dual" licensing schemes that I know many developers are using and
that I've recently switched to. This is for apps that, after
validating a user's serial number, download the "real" license file
(for example, an AquaticPrime file) in the background and store it as
the actual unlocking mechanism for the app. Again, feel free to email
with any questions on getting all of this working in your own setup.

Finally, going hand in hand with the in-app licensing stuff, Shine has
a new "Activations" tab for those of you whose apps phone-home to
validate license files.

Cheers.
Tyler