Some of the email providers (like GMail and Fastmail) save Sent messages
automatically, so make the folders optional in the configuration.
Make Drafts folder optional as well, to allow it to be configured
manually in the extraConf with location outside of the maildir.
Alot uses the first email in the config as primary email. Because the
order in which the email.accounts were sorted was alphabetical, the account
set to `primary = true` was not put first in the alot config and thus
not considered as primary email for alot.
This was fixed by sorting the email accounts again such that accounts
with `primary = true` come first.
