Add subcommand for import and export of custom queries

[exploide]

BloodHound CE supports storing custom Cypher queries. However, there is currently no convenient way to import and export them. bhcli can get a subcommand which allows importing and exporting custom queries via the API.

There are multiple BloodHound CE issues showing a need for this:

• [Feature Request] Ability to save & export settings and custom queries SpecterOps/BloodHound#18
• Import custom queries from Legacy Bloodhound SpecterOps/BloodHound#241
• custom queries SpecterOps/BloodHound#558

[exploide]

Implemented import/export in the queries subcommand:

$ bhcli queries my-bloodhound-queries.json
INFO: Imported 12 custom queries.

The import file must either be in the format that the --save option produces or in the legacy Bloodhound's customqueries.json format.
Note that not everything from the latter might be compatible.