Improve big picture flow

[wrtsprt]

• closes (at least) https://github.com/brug-be/railsgirls_guide/issues/36
• closes https://github.com/brug-be/railsgirls_guide/issues/29 - we no need for moving the page anymore, we will just copy / paste the content
• closes https://github.com/brug-be/railsgirls_guide/issues/7
• closes https://github.com/brug-be/railsgirls_guide/issues/8

This PR improves the big picture flow for part 2. We came across some inconsistencies and structural problems in the old version, which basically needed a rewrite iso of small changes.

The high level flow of the new version is:

• show rails
• use the scaffold
• then add the about page from part 1 (iso of starting with it and having to awkwardly copy it twice)
• then showing how erb works
• then adding another model

Since it's a bigger change, I think the diff is not going to be of much help. It's probably better to just read through the new version.

The rest of part two is untouched to keep the scope of this PR as small as possible. There are still many things to improve. I will put into separate tickets.

[borisrorsvort]

Since the title seams very large, can you add your vision regarding this Pr in the description, will be easier to review afterwards ;) I would also reach out to @vanakenm as he will most likely be in the next board and propose a direction for the next upcoming events.

[borisrorsvort]

Thanks for taking a stab at this btw :)

[wrtsprt]

Who's up for reviewing this? @borisrorsvort, @vanakenm, @otagi? Anyone else?