Review and update Validations doc

[lread]

Re-organize and re-section.

Add some info on exit codes.

Add a screenshot to show an example of ws get:messages.

Update Warning 206 screenshot to what it should be now: Error 111.

Turf note on Warning 207 that it is only be applied to check command, it's not true anymore.

Configuration doc:

• the only reason we documented :bricks was to describe disabling Error 111, this is no longer a feature so we no longer need to describe :bricks.
• correct description for :necessary and add link to Validations doc.

Edits for clarity.

[lread]

@tengstrand, ready for review and feedback. As always, please read the commit message first.

[lread]

@tengstrand review feedback addressed.