Support JW Player plugins

I've spoken with colleagues about this functionality. Notes from the conversation are below:

The JW Player module is meant to be a "generic" module that can be used as the base for any JW Player implementation. As such it would not be appropriate to implement specific plugins such as GA Pro and not others. Instead the JW Player module should provide a flexible API that allows other modules to register JW plugins on their own. At this point we could potentially register popular plugins from with the module itself by implementing the modules own API, but it would be just as simple to implement the relevant hook(s) from a module such as jw_player_ga_pro.

Specifically we spoke about a hook such as hook_jw_player_plugin_info() (or alternately hook_jw_player_plugin_register() or just hook_jw_player_plugin()). This hook would allow any module to register a plugin and all of its available configuration options with JW Player. The array format would be something like this:

$plugins['ga_pro2'] = array(
	'name' => 'Google Analytics Pro',
	'description' => t('A description of the plugin'),
	'config_options' => array(
		'trackstarts' = array(
			'name' => t('Track when videos start playing'),
			'allowed_values' = array('true, false'),
		)
		'key2' = array(
			'name' => "Human readable version of this configuration option",
			'allowed_values' = array('mode1', 'mode2', 'mode3', 'mode4'),
		)
	)
);

The human readable text for the plugin and configuration would be made available from within the presets form. This could be accomplished by calling something like jw_player_plugins_load(), which would fire the hook implementations and return all registered plugins. From this information the preset configuration form could be created. Which plugins are enabled and the settings for each plugin would be saved as part of a preset.

When rendering the player itself the configuration would be added to the JW player configuration as follows:

'plugins': {
   'gapro-2': {
       'trackstarts': 'true',
       'key2': 'mode4',
       'tracktime': 'false'
   }
   'another-plugin': {
       'foo': 'true',
       'bar': 'baz',
   }
}

While we have a fairly good idea of what needs to be accomplished many questions remain:

• The JW Player module for Drupal 6 used XML based configuration. Was there a specific reason for this? Is this is a standard format? It is worth investigating to see what is the best approach. Nested PHP arrays are naturally "Drupally" but we also want to follow any JW Player standards that exist.
• How should local plugins not hosted with Longtail video be loaded, if at all?
• How do we handle JW Player account ids and access to specific plugins covered by one's license?
• Some plugins such as the HD player require a configuration values that are unique for every video, meaning that they can not be configured via the preset. Do we provide a callback for preset values, handle this via pre-process or solve in some other fashion?

@Girish The code looks good. Committed! Let's continue to monitor the architecture for plugins as additional use cases come up. At the moment reworking #1318342: Add support for Closed captions and Audio Descriptions to use this new plugin API would be an excellent test case.