Project 2022-12-055, task 3: Add write-functionality to the e-mail client

[BjarniRunar]

The goal of this task is to flesh out the required back-end API methods and deliver a text-mode tool which is capable of modifying the contents of a local or remote mailbox; adding, moving or deleting mail.

Milestone(s):

• Update all mail source code with write/delete functions
• Create logic which allows "delete from server after a period of time has passed", like Mailpile v1
• Document how to use relevant moggie APIs from the CLI or as a web API