Implement other endpoints

[xakraz]

PyPuppetDB implement mainly the pdb/query/ endpoint.

It would be nice to have the others alos:

• https://puppet.com/docs/puppetdb/4.4/api/admin/v1/cmd.html
• https://puppet.com/docs/puppetdb/4.4/api/command/v1/commands.html
• ...

[nmaludy]

+1

[othalla]

@xakraz @nmaludy do you have some time to write the code?