Various QoL fixes for Desktop App (#2999)

* Some ESLint fixes

* Add login/logout signal to API, clear mentions on logout and flush cookies on login/logout

* Fix issue where local and HTTP-only servers would not validate correctly

* Reduce noise of renderer logging, adjust a few local renderer logs to be louder when needed

* Fallback to beginning of hostname for servers that don't change the site name

* Fix Save Image crash

* Update the name for insecure servers too

* Fix test

* Fix lint

* Reduce repetition

api-types/lib/index.d.ts

@@ -20,6 +20,8 @@ export type DesktopAPI = {
     reactAppInitialized: () => void;
     setSessionExpired: (isExpired: boolean) => void;
     onUserActivityUpdate: (listener: (userIsActive: boolean, idleTime: number, isSystemEvent: boolean) => void) => () => void;
+    onLogin: () => void;
+    onLogout: () => void;
     sendNotification: (title: string, body: string, channelId: string, teamId: string, url: string, silent: boolean, soundName: string) => Promise<{
         result: string;
         reason?: string;