More progress on tab-complete

There are missing parts to the "account-based" emotes that needs to be
completed before emote completion can be considered done. For now, when
I've been testing, I've been manually injecting the oauthClient and
oauthToken to the settings file with the `user_subscriptions` scope

src/widgets/notebook.cpp

@@ -1,5 +1,6 @@
 #include "widgets/notebook.hpp"
 #include "colorscheme.hpp"
+#include "widgets/mainwindow.hpp"
 #include "widgets/notebookbutton.hpp"
 #include "widgets/notebookpage.hpp"
 #include "widgets/notebooktab.hpp"
@@ -18,9 +19,10 @@
 namespace chatterino {
 namespace widgets {
 
-Notebook::Notebook(ChannelManager &_channelManager, BaseWidget *parent)
+Notebook::Notebook(ChannelManager &_channelManager, MainWindow *parent)
     : BaseWidget(parent)
     , channelManager(_channelManager)
+    , completionManager(parent->completionManager)
     , addButton(this)
     , settingsButton(this)
     , userButton(this)