allow to change primary color

Castellum is an internal tool, so there are not many requirements in terms of CI. Therefore we chose to stick to the bootstrap design framework and not write much CSS of our own.

Recently, some use cases came up for allowing more theming:

• An insitute may for some reason have more than one installation of castellum. Theming could be used to avoid confusion as to which installation a user is currently using.
• Castellum itself is internal, but the scheduler is external and currently also uses stock bootstrap.

My proposal is to stay with bootstrap, but overwrite its primary color:

Bootstrap provides several ways to achieve this:

• CSS custom properities: It would be great if we could just change a few custom properties. Unfortunately they are not used in a way that would allow that.
• Scss variables: This would require us to include a Scss compiler somewhere in our build process which I would like to avoid.
• overwrite CSS: This is the approach that I took. However, it is brittle because the underlying bootstrap code might change.

I am also thinking about moving this to an external package so it can be reused among our projects.

So the question is: Do the use cases justify a feature that might cause quite some maintenance work?