Active Model Record Implementation

This is a pretty simple concept, in most occasions, there is a particular record that defines the current request (whether that is the currently logged-in user, the current post you are looking at, or the current category, etc.).

Basically this gives the ability to load once that active record, cache it, and easily and quickly load it in the the future.

Example:

```
Model_Post::find(1234)->set_active_record();
Model_User::find(321)->set_active_record();
```

That data is then stored the the model class and is then can be extremely easily recalled like so:

```
echo Model_Post::active_record()->name;
echo Model_User::active_record()->get_full_name();
```

There is almost no code involved in this, but I make sure to put it into every fuel project I work on.  It makes working on projects like this extremely fluid.