Description:

Manuskript 0.12.0 crashes on startup. Version 0.13.1 works correctly.

```
CRITICAL> An unhandled exception has occurred!
Traceback (most recent call last):
File "/usr/bin/manuskript", line 30, in <module>
main.run()
File "/usr/share/manuskript/manuskript/main.py", line 291, in run
app, MW = prepare(arguments)
File "/usr/share/manuskript/manuskript/main.py", line 170, in prepare
from manuskript.mainWindow import MainWindow
File "/usr/share/manuskript/manuskript/mainWindow.py", line 23, in <module>
from manuskript.models.worldModel import worldModel
File "/usr/share/manuskript/manuskript/models/worldModel.py", line 11, in <module>
from manuskript.ui import style as S
File "/usr/share/manuskript/manuskript/ui/style.py", line 36, in <module>
highlightLight = F.mixColors(highlight, window, .3)
File "/usr/share/manuskript/manuskript/functions/__init__.py", line 197, in mixColors
return QColor(r, g, b) if not fromString else QColor(r, g, b).name()
TypeError: arguments did not match any overloaded call:
QColor(Qt.GlobalColor): argument 1 has unexpected type 'float'
QColor(int): argument 1 has unexpected type 'float'
QColor(QRgba64): argument 1 has unexpected type 'float'
QColor(Any): too many arguments
QColor(): too many arguments
QColor(int, int, int, alpha: int = 255): argument 1 has unexpected type 'float'
QColor(str): argument 1 has unexpected type 'float'
QColor(Union[QColor, Qt.GlobalColor, QGradient]): argument 1 has unexpected type 'float'
```

Steps to reproduce:
* `manuskript`
* see crash