Support parsing matrix.to links in the timeline with ?via= in them

This ends up being translated to ?server_name= in the matrix-js-sdk, although that has a bug at the time of writing. It converts `server_name: ['a', 'b']` to `?server_name=a,b` instead of `?server_name=a&server_name=b`

For reference: the `viaServers` option is routed through the 'join_room' action to RoomViewStore#_joinRoom which is passed directly to the js-sdk http-api#joinRoom function.

Next steps:
* Fix the js-sdk parsing
* Make the SDK generate matrix.to links with ?via=

src/components/structures/LoggedInView.js

@@ -64,6 +64,9 @@ const LoggedInView = React.createClass({
 
         teamToken: PropTypes.string,
 
+        // Used by the RoomView to handle joining rooms
+        viaServers: PropTypes.arrayOf(PropTypes.string),
+
         // and lots and lots of other stuff.
     },
 
@@ -389,6 +392,7 @@ const LoggedInView = React.createClass({
                         onRegistered={this.props.onRegistered}
                         thirdPartyInvite={this.props.thirdPartyInvite}
                         oobData={this.props.roomOobData}
+                        viaServers={this.props.viaServers}
                         eventPixelOffset={this.props.initialEventPixelOffset}
                         key={this.props.currentRoomId || 'roomview'}
                         disabled={this.props.middleDisabled}

src/components/structures/MatrixChat.js

@@ -840,6 +840,7 @@ export default React.createClass({
             page_type: PageTypes.RoomView,
             thirdPartyInvite: roomInfo.third_party_invite,
             roomOobData: roomInfo.oob_data,
+            viaServers: roomInfo.via_servers,
         };
 
         if (roomInfo.room_alias) {
@@ -1488,9 +1489,21 @@ export default React.createClass({
                 inviterName: params.inviter_name,
             };
 
+            // on our URLs there might be a ?via=matrix.org or similar to help
+            // joins to the room succeed. We'll pass these through as an array
+            // to other levels. If there's just one ?via= then params.via is a
+            // single string. If someone does something like ?via=one.com&via=two.com
+            // then params.via is an array of strings.
+            let via = [];
+            if (params.via) {
+                if (typeof(params.via) === 'string') via = [params.via];
+                else via = params.via;
+            }
+
             const payload = {
                 action: 'view_room',
                 event_id: eventId,
+                via_servers: via,
                 // If an event ID is given in the URL hash, notify RoomViewStore to mark
                 // it as highlighted, which will propagate to RoomView and highlight the
                 // associated EventTile.

src/components/structures/RoomView.js

@@ -88,6 +88,9 @@ module.exports = React.createClass({
 
         // is the RightPanel collapsed?
         collapsedRhs: PropTypes.bool,
+
+        // Servers the RoomView can use to try and assist joins
+        viaServers: PropTypes.arrayOf(PropTypes.string),
     },
 
     getInitialState: function() {
@@ -833,7 +836,7 @@ module.exports = React.createClass({
                 action: 'do_after_sync_prepared',
                 deferred_action: {
                     action: 'join_room',
-                    opts: { inviteSignUrl: signUrl },
+                    opts: { inviteSignUrl: signUrl, viaServers: this.props.viaServers },
                 },
             });
 
@@ -875,7 +878,7 @@ module.exports = React.createClass({
                 this.props.thirdPartyInvite.inviteSignUrl : undefined;
             dis.dispatch({
                 action: 'join_room',
-                opts: { inviteSignUrl: signUrl },
+                opts: { inviteSignUrl: signUrl, viaServers: this.props.viaServers },
             });
             return Promise.resolve();
         });