[MM-36421] Replace server tabs with dropdown menu (#1647)

* WIP

* WIP

* PoC for dropdown - logic stuff

* Most of the logic for the dropdown

* Working dropdown menu to pick servers

* Mentions, unreads and expired working. Many styles are working.

* Some more styles

* Dark mode and other stuff

* Some cleanup

* Generate build

* PR feedback

* More PR feedback

webpack.config.main.js

@@ -18,6 +18,7 @@ module.exports = merge(base, {
     entry: {
         index: './src/main/main.ts',
         mainWindow: './src/main/preload/mainWindow.js',
+        dropdown: './src/main/preload/dropdown.js',
         preload: './src/main/preload/mattermost.js',
         modalPreload: './src/main/preload/modalPreload.js',
         loadingScreenPreload: './src/main/preload/loadingScreenPreload.js',