TTE wglc redo

[mcr]

TTE sent a pull request at: #40 but it contained many unrelated changes in a single git commit, which made it very hard to evaluate. This contains the group of mostly non-controversial commits.
The changes to the time-sequence diagrams are not included.

[EskoDijk]

Agree to merge these! I did find some typos but I prefer to fix these in separate PRs later on to get this content included as quickly as possible. It clarifies quite a bit better, compared to the original text.