Move VAPID public key config to backend for easier config

Also enables the frontend not asking for notiffication permission if it
doesn't need them.
Should also help if it ever needs to be changed to circumvent cache.

web/main.js

@@ -1,5 +1,3 @@
-var pushServerPublicKey = 'BBwBPYxhogHLU3B1FpxfQNzO3q7qZpmD1n1KaaL8WJbcVmJSHhi1uB-VmvsVjjUHWYCeqKyLT7w-1LBfpIcbbcg'
-
 var spage = document.getElementById('startpage')
 var mform = document.getElementById('mainform')
 
@@ -226,6 +224,18 @@ function initPush(name) {
 		return
 	}
 
+	fetch('/pushinfo').then(function(res) {
+		if (res.ok)
+			res.json().then(function(push) {
+				if (push.enabled)
+					registerPush(name, push.publickey);
+			});
+	});
+
+}
+
+function registerPush(name, pushServerPublicKey) {
+
 	// Register service worker
 	navigator.serviceWorker.register("/sw.js").then(function(swRegistration) {
 		console.log("ServiceWorker registered:", swRegistration)