core: Automatically select a bridge based on a URL (#928)

* core: Add bridge parameter auto detection

This adds a new 'detect' action which accepts a URL from which an
appropriate bridge is selected and relevant parameters are extracted.
The user is then automatically redirected to the selected bridge.

For example to get a feed from: https://twitter.com/search?q=%23rss-bridge
we could send a request to:
'/?action=detect&format=Atom&url=twitter.com/search%3Fq%3D%2523rss-bridge'
which would redirect to:
'/?action=display&q=%23rss-bridge&bridge=Twitter&format=Atom'.

This auto detection happens on a per-bridge basis, so a new function
'detectParameters' is added to BridgeInterface which bridges may implement.
It takes a URL for an argument and returns a list of parameters that were
extracted, or null if the URL isn't relevant for the bridge.

* [TwitterBridge] Add parameter auto detection

* [BridgeAbstract] Add generic parameter detection

This adds generic "paramater detection" for bridges that don't have any
parameters defined. If the queried URL matches the URI defined in the
bridge (ignoring https://, www. and trailing /) an emtpy list of parameters is
returned.

lib/BridgeInterface.php

@@ -114,4 +114,12 @@ interface BridgeInterface {
 	 * @return int Cache timeout
 	 */
 	public function getCacheTimeout();
+
+	/**
+	 * Returns parameters from given URL or null if URL is not applicable
+	 *
+	 * @param string $url URL to extract parameters from
+	 * @return array|null List of bridge parameters or null if detection failed.
+	 */
+	public function detectParameters($url);
 }