GUACAMOLE-300: Support posixGroup in LDAP Authentication and Group-based Session Admission

reset/rebase/squash a chaos of commits:
- implement user/group membership search using Apache Directory Ldap module instead of JLDAP
- Retrieve user's group membership if specified by username rather than DN
- New enum 'MemberAttributeType'
- New GuacamoleProperty 'MemberAttributeTypeProperty'
- New configuration property 'ldap-member-attribute-type'
    Specifies what the field specified by 'ldap-member-attribute' actually
    contains -- "dn" (default) or "uid" or ...
5 files changed