[doc] missing import in code example

[doc] add a note because uiprops.py is not generated anymore by default

[doc] recommend pip instead of apt for installing things According to a discussion on XMPP we should recommend pip instead.

[doc] fix, link to internal doc since it's not the blog post anymore

[doc] also show command with sqlite since it's recommended

[doc] fix, the cube name was used, it was the instance named that was needed

[doc] it's a tutorial, not a blog post anymore

[doc] make example more redable

[doc] uses :file:`name` everywhere + indicate file when it's not present

[doc] english typos

[doc] pep8/retab in code examples

[doc] correct import for i18n

[doc] pep8 and retab in tutorial code example

[doc] correct pip command to have needed dependancies to use the start command I know we want to remove this command but in the meantime having this documentation working seems like something good.

[doc] explain the difference between a relation and an attribute