Groups2

[Paul-Ferrell]

Code review checklist:

• Code is generally sensical and well commented
• Variable/function names all telegraph their purpose and contents
• Functions/classes have useful doc strings
• Function arguments are typed
• Added/modified unit tests to cover changes.
• New features have documentation added to the docs.
• New features and backwards compatibility breaks are noted in the RELEASE.md

[francinelapid]

Found an issue where I tried to use pav group remove 15 s1 to remove test 15 and series 1 but it was unable to remove test 15

 $ pav group remove test2 15 s1
There were one or more errors when removing tests.
Given test '15' to remove, but it is not in group 'test2'.
Removed 1 item.