Gbpcli

This release adds the ability to choose a custom config file location via a `GBPCLI_CONFIG` environment variable.

This release addresses issues encountered while going through the [Install Guide](https://github.com/enku/gentoo-build-publisher/blob/master/docs/how-to-install.md#gentoo-build-publisher-install-guide).

Notable changes:

- Add support for config files
- Send API key in GraphQL queries if configured

Notable changes:

- The build subcommand can now pass build parameters to Jenkins
- Command-line (tab) completion support
- The queries interface is now namespaced. This helps developing gbpcli plugins

This release is mostly internal improvements/fixes.

Notable user-facing changes are:

- The pull subcommand learned the ability to pull with a note, for
example `gbp pull --note "Built with --emptytree" babette 999`
- Unknown theme names are no longer disregarded. This is to allow for
third-party subcommands, (e.g. `gbp-ps`) to have their own theme
names.