Webatrice: fix login bugs (#4557)

* fix login after failed connection attempts, limit connection attempt time

* fix register hashed password and salt

* add feature detection and Unsupported Browser screen

* nit

Co-authored-by: Jeremy Letto <jeremy.letto@datasite.com>

webclient/src/services/dexie/DexieService.ts

@@ -28,6 +28,10 @@ class DexieService {
   get hosts() {
     return this.db.table(Stores.HOSTS);
   }
+
+  testConnection() {
+    return this.db.open();
+  }
 }
 
 export const dexieService = new DexieService();

webclient/src/services/dexie/index.ts

@@ -1 +1,2 @@
 export * from './DexieDTOs';
+export * from './DexieService';