[DOCS0-2] Documentation improvements for 0.2.0 release.

[blythed]

We would like to bring the docs up-to-date according to the results of the discussion here

Tasks:

• [ ] Get feedbacks
• [x] Decide new structure
• [ ] Add snippets on the quickstart of the blog
• [x] Optimize the title of the Community Support on the docs - and other ones if it's needed
• [x] #1757
• [x] Nest all the databases under one menu
• [x] Nest the fundamentals in meaningful categories
• [x] Merge components and component versioning together
• [x] Group pages in the walkthrough
• [x] Group the use-cases properly
• [ ] Discussion about the notebooks place
• [ ] Test the user-case to remove obsolete versions and code ( This should be an issue and not a task)
• [x] #1854
• [ ] #1857
• [x] #1874
• [x] #1876
• [x] #1880
• [x] #1949
• [ ] #1950
• [x] #1951
• [x] #1956
• [ ] #2014