[Feature] Support Restricted Access Types

[0xTowel]

Support to create and change changelists with the restricted access type would be helpful.

Changelist Type: (or "Access type" in P4V) is writable, optional type for changelists which is allowed to be either restricted or public.

A restricted shelved or committed change is only accessible to users who own the change or have list permissions to at least one file in the change. Public changes are disabled with restrictions.

My attempt to support this in python-perforce is in PR #42