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.

index.php

@@ -96,6 +96,42 @@ try {
 		header('Content-Type: application/json');
 		echo json_encode($list, JSON_PRETTY_PRINT);
 
+	} elseif($action === 'detect') {
+
+		$targetURL = $params['url']
+			or returnClientError('You must specify a url!');
+
+		$format = $params['format']
+			or returnClientError('You must specify a format!');
+
+		foreach(Bridge::listBridges() as $bridgeName) {
+
+			if(!Bridge::isWhitelisted($bridgeName)) {
+				continue;
+			}
+
+			$bridge = Bridge::create($bridgeName);
+
+			if($bridge === false) {
+				continue;
+			}
+
+			$bridgeParams = $bridge->detectParameters($targetURL);
+
+			if(is_null($bridgeParams)) {
+				continue;
+			}
+
+			$bridgeParams['bridge'] = $bridgeName;
+			$bridgeParams['format'] = $format;
+
+			header('Location: ?action=display&' . http_build_query($bridgeParams), true, 301);
+			die();
+
+		}
+
+		returnClientError('No bridge found for given URL: ' . $targetURL);
+
 	} elseif($action === 'display' && !empty($bridge)) {
 
 		$format = $params['format']