Fix the naming of contactgroup and contactgroup_member

[ncosta-ic]

Currently, the PostgreSQL schema uses the snake_case notation and distinguishes between basic data and data additions.
Examples:

• Table contact => Holds the basic information for a contact/user.

• Table contact_address => Holds additional information about a contact's address data.

• Table incident => Holds the basic information for an incident.

• Table incident_contact => Holds additional information about what contacts are associated with the incident.

This notation is used everywhere, with the exception of the contactgroup. As this table holds basic information about the group itself, it's not directly associated with a contact. That only happens if a contact gets its relation assigned in the contactgroup_member table.
Thus I would suggest to either change the table names contactgroup and contactgroup_member to just group and group_member or to add an additional underscore to emphasize their distinctions (contact_group and contact_group_member in that case).