This allows pages to be to redirect any url, anywhere, even when not
in a page context.

identifiers by a custom scheme and rename 'pages' scheme to 'page'

The callback is defined is as follows: 'function($route, $generate = false)'

- $route: a ComPagesDispatcherRouteRouteInterface object
- $generate: are we generating a url or resolving (default false)

Callbacks are both supported for static and dynamic routes, in case of a
dynamic route the callback is called only if the route could be succesfully
resolved.

Example:

'/path/to/page' => [
	'generate' => function($route)
	{
		return true;
	},
	'resolve' => function($route)
	{
		return true;
	}
],

…r redirect method

- Add 'slug' expression constraint
- If the target contains a contraint the target segment will be filtered acoordingly

- Add 'id' type
- Do not use a match group for 'slug' type

# Conflicts:
#	code/site/components/com_pages/dispatcher/http.php
#	code/site/components/com_pages/resources/config/site.php