Update linux, make and cmake basics

[uekerman]

Description

Update the "linux, make, cmake" lecture and exercise. For CMake, I added a few additional tricks I got from Code Refinery.

Checklist

• [x] I made sure that the markdown files are formatted properly.
• [x] I made sure that all hyperlinks are working.

[MakisH]

What is the expected order of the slides? I think the list in the README.md does not correspond to this year's schedule.

Also: What was already covered last week?

[uekerman]

Order is given by the timetable. README should be alphabetically. It's:

1. linux
2. make
3. cmake basics