Huge refactor

- Remove some underscore-prefixes
 - Start using this-> more
 - Remove a few of the singletons (We pass references to managers to
         things that need it now. Might not be much better, but for now
         it works. It also shows what places might be slightly wrong
         designed)

src/windowmanager.cpp

@@ -1,5 +1,6 @@
 #include "windowmanager.hpp"
 #include "appdatapath.hpp"
+#include "channelmanager.hpp"
 
 #include <QDebug>
 #include <QStandardPaths>
@@ -7,10 +8,9 @@
 #include <boost/property_tree/json_parser.hpp>
 
 namespace chatterino {
-WindowManager WindowManager::instance;
 
-WindowManager::WindowManager()
-    : _mainWindow(nullptr)
+WindowManager::WindowManager(ChannelManager &_channelManager)
+    : channelManager(_channelManager)
 {
 }
 
@@ -23,41 +23,41 @@ static const std::string &getSettingsPath()
 
 void WindowManager::layoutVisibleChatWidgets(Channel *channel)
 {
-    if (_mainWindow != nullptr) {
-        _mainWindow->layoutVisibleChatWidgets(channel);
+    if (this->mainWindow != nullptr) {
+        this->mainWindow->layoutVisibleChatWidgets(channel);
     }
 }
 
 void WindowManager::repaintVisibleChatWidgets(Channel *channel)
 {
-    if (_mainWindow != nullptr) {
-        _mainWindow->repaintVisibleChatWidgets(channel);
+    if (this->mainWindow != nullptr) {
+        this->mainWindow->repaintVisibleChatWidgets(channel);
     }
 }
 
 void WindowManager::repaintGifEmotes()
 {
-    if (_mainWindow != nullptr) {
-        _mainWindow->repaintGifEmotes();
+    if (this->mainWindow != nullptr) {
+        this->mainWindow->repaintGifEmotes();
     }
 }
 
 void WindowManager::updateAll()
 {
-    if (_mainWindow != nullptr) {
-        _mainWindow->update();
+    if (this->mainWindow != nullptr) {
+        this->mainWindow->update();
     }
 }
 
 widgets::MainWindow &WindowManager::getMainWindow()
 {
-    std::lock_guard<std::mutex> lock(_windowMutex);
+    std::lock_guard<std::mutex> lock(this->windowMutex);
 
-    if (_mainWindow == nullptr) {
-        _mainWindow = new widgets::MainWindow();
+    if (this->mainWindow == nullptr) {
+        this->mainWindow = new widgets::MainWindow(this->channelManager);
     }
 
-    return *_mainWindow;
+    return *this->mainWindow;
 }
 
 void WindowManager::load()