Fix the stupid things.

This includes:
 - NuulsUploader.cpp
   - changing upload delay to a #define
   - moving png conversion code to `boost::optional<QByteArray> convertToPng(QImage image)`
   - in uploadImageToNuuls: moving content type definition to a variable, move things around a bit to eliminate an if
   - in upload: adding a comment about `source->hasUrls()` and `source->urls()`, change `uploadQueue.size()` to `!uploadQueue.empty()`
 - ResizingTextEdit.cpp
   - changing #include order

src/widgets/helper/ResizingTextEdit.cpp

@@ -1,9 +1,10 @@
-#include <QMimeData>
+#include "widgets/helper/ResizingTextEdit.hpp"
 
 #include "common/Common.hpp"
 #include "common/CompletionModel.hpp"
 #include "singletons/Settings.hpp"
-#include "widgets/helper/ResizingTextEdit.hpp"
+
+#include <QMimeData>
 
 namespace chatterino {