Proposals to plan events

[forrestwilkins]

Add ability to plan events via proposals in groups. Users should be able to specify time and date, location, etc.

old-praxis can be used as a reference: https://github.com/forrestwilkins/praxis-old

Depends on:

• https://github.com/praxis-app/praxis-ui/issues/39
• https://github.com/praxis-app/praxis-api/issues/87