Upgrade editor

The script editor lacks some functionality, which was identified when users who are not proficient in Python were using it. Mostly, they ran into small syntax errors. This PR, therefore, adds a flake8-based syntax checker that checks the current editor every second and indicates issues on the respective lines. A find-and-replace widget was also added to make it easier to navigate the scripts.

There was also a small issue with f-strings not being displayed correctly, which has been addressed.