Initial support for Google Calendar

[PortableProgrammer]

• Adds Google Calendar support (closes Add support for Google Calendar #47).
• As part of this addition, had to refactor the directory structure to be more consistent with Python package standards (closes Refactor directory structure to Python standards #52), since the google module was in conflict between internal and external sources.
• As a further part of this addition, updated the documentation to begin referring to collaboration and calendar status sources instead of the explicit Webex and Office 365 sources (closes Refer to 'collaboration' and 'calendar' sources instead #53), since we now have multiple calendar sources.
• This PR also includes public OAuth2 Google API keys (status-light/utility/api/calendar/google/client_secret.json), which should not be treated as secrets in this case; they are linked to a public readonly application that will only request the https://www.googleapis.com/auth/calendar.readonly scope.