Consistent format in examples

[thomasp85]

This PR ensures consistency in how we format ggsql code in examples.

The rules (which we should follow onwards) are:

1. 2-space tab widrth
2. Main clauses are never indented
3. subclauses gets on a new line, indented
4. Certain subclauses are exempt from this:

• FROM, TO, VIA in SCALE
• TO in `PROJECT``

5. If content of a subclause cannot fit in a line it goes on a new line and is separated at commas
6. Blank line between SQL query and VISUALISE