feat: hand in file/line to generic line template

[phikes]

This PR hands in the file and line objects into the "generic-line" template as variable. See this issue for more context.

Some of the questions here include:

• are the tests enough like this or should we add tests for overwriting templates which consume these variables?
• Should we hand in the "main entity" (or entities) to other templates as well? (I only needed the file/line in the generic line template)

Thanks again for being friendly and open about my issue and proposal! :-)

[phikes]