We already kept track of the file and widget CSS was read from. Now, we also keep track of the class variable it comes from and we create some structure to transfer that information across the program.

Instead of creating the link explicitly, we let terminal emulators auto-link to the file.
This came after a discussion about how/whether we should try to support linking to specific file lines/columns for TCSS files and after some research to see how that would be possible.
We decided to drop this feature when we couldn't find information in the standards for 'file://' regarding how to specify line/column numbers and after we found [this iTerm issue](https://gitlab.com/gnachman/iterm2/-/issues/9376) where the creator/maintainer of iTerm says that there is no standard API for opening a file to a particular line number.