feat(auth): Add optional CSRF protection (#697)

* fix(auth): Missing CSRF middleware
Resolves LGTM alert/error for query js/missing-token-validation
More info: https://lgtm.com/rules/1506064038914/

server/lib/settings.ts

@@ -48,6 +48,7 @@ export interface SonarrSettings extends DVRSettings {
 export interface MainSettings {
   apiKey: string;
   applicationUrl: string;
+  csrfProtection: boolean;
   defaultPermissions: number;
   hideAvailable: boolean;
 }
@@ -155,6 +156,7 @@ class Settings {
         apiKey: '',
         applicationUrl: '',
         hideAvailable: false,
+        csrfProtection: false,
         defaultPermissions: Permission.REQUEST,
       },
       plex: {