Make sgh api look much more like gh

[Ultramann]

This PR lays the groundwork for building out sgh to have close parity with gh. In particular it

• fixes hack to get pr/issue count by using the search api
• adopts gh's subcommand naming and information outputted for existing functionality
• stops calling the api twice one for auth checking, by implementing auth error parsing on the single api call
• adds a function to format data as a table
• adds json output flag, --json, implemented with new graphql query generation and running