correct action hook for register_admin_styles

Changed the action hook from 'admin_print_styles' to 'admin_enqueue_scripts' which is better.

See: http://codex.wordpress.org/Plugin_API/Action_Reference/admin_enqueue_scripts

See: http://make.wordpress.org/core/2011/12/12/use-wp_enqueue_scripts-not-wp_print_styles-to-enqueue-scripts-and-styles-for-the-frontend/
Removed the need to customize url for wp_enqueue_style and wp_enqueue_scripts

By adding the __FILE__ magic constant as a second parameter to the wp_enqueue_style and wp_enqueue_scripts, the user no longer needs to change 'plugin-name'. This also makes the code more robust.
Added Plugin Settings page (commented out)

Added a Plugin Settings page, that can be enabled by uncommenting the line that hooks it into the admin_menu action hook.

Added additional views that contain the WordPress standard markup to wrap the plugin settings markup.

The views are now loaded into the plugin page.
Restricted scripts and styles to load only on plugin settings page if it is enabled.

If the Settings page has been activated, the scripts and styles will only be loaded on the settings page. If not, they will be loaded for all admin pages (like before this commit)

Also added the __FILE__ magic constant as a second parameter to the admin_enqueue_style and admin_enqueue_script, the user no longer needs to change 'plugin-name'. This also makes the code more robust.
Merge pull request #27 from mikkelbreum/master

improvements and additions (added settings page)