websocket: don't handle target=_blank links

For https://github.com/srid/emanote/issues/129

CHANGELOG.md

@@ -10,6 +10,7 @@
   - Scroll to top on route switches
   - Use secure websockets when on HTTPS
   - Bind to loopback (127.0.0.1) for security reasons
+  - Do not handle target=_blank links in websocket route switch
 - `Asset` type
   - Introduce the `Asset` type to distinguishing between static files and generated files. The later can be one of `Html` or `Other`, allowing the live server to handle them sensibly.
   - `Ema` typeclass: 

src/Ema/Server.hs

@@ -273,7 +273,7 @@ wsClientShim =
           function handleRouteClicks(e) {
               const origin = e.target.closest("a");
               if (origin) {
-                if (window.location.host === origin.host) {
+                if (window.location.host === origin.host && origin.getAttribute("target") != "_blank") {
                   window.history.pushState({}, "", origin.pathname);
                   switchRoute(origin.pathname);
                   e.preventDefault();