Allow configuration from controller and/or view (and still support legacy geshi.php config file).

This is a resubmission of a previous pull request with updated code that allows setting GeSHi options from either the controller (in the $helpers array) or in the view (via the exposed GeSHi instance).

Unlike the previous request this release still allows the use of the geshi.php config file. It will be overridden as soon as one of the other methods are used, allowing for a good transitions for implementors.

1. geshi.php is used.
2. Developer adds configuration in his views where appropriate, overriding the file for those views.
3. File still provides legacy configuration in instances where developer hasn't added controller or view configuration.