pin sphinx-copybutton and change config

pin sphinx-copybutton and change config

sphinx-copybutton introduced a new feature
in 0.5.1 which includes a default configuration
that breaks the regexp prompt matching scheme.

set copybutton_exclude to not include ".gp" as that's the class
where we exactly look for the prompts we are matching.
While we're there, use this new feature to exclude our sql
styles, even though this is not strictly necessary in our case.

pin sphinx-copybutton at 0.5.1 to avoid future problems.

Change-Id: I8eaeab13995c032b9ee3afd1f08dae5929009d45
References: https://github.com/executablebooks/sphinx-copybutton/issues/185