Add Proposify as a connector

[MitchC3]

Proposify would make a great addition to Flow's connectors.

Triggers: When a propsoal is created/updated/approved/declined/commented on/viewed/sent

Actions: Create a proposal/client/contact, update a proposal/client/contact, get a proposal/client/contact

Zapier has Proposify as a connector, but it isn't as fully flushed out as it could be.