alot: cleanup sorting messages of thread
alot: cleanup sorting messages of thread

notmuch returns threads and messages sorted purely on the `Date`-header.
When a thread contains non-compliant mails without the header, they are
considered to be sent at beginning of epoch. `get_date` does consider
the `Received` headers though. Threads are usually small enough to make
sorting the individual messages in python acceptable. They are loaded
anyway.

paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles