Clear mailboxes list before its assignment.

On account change new account's mailboxes are being appended to the old
one's. This commit forces mailboxes list to be cleared before adding new
items to it.

Untrack personal.muttrc

This commit untracks personal.muttrc and moves the import of
personal.muttrc to the last line of muttrc. I did this for several
reasons:

1. I moved the personal.muttrc import to have the possibility to
   overwrite settings made in muttrc. This makes personalizing mutt
   easier.
2. Since personal.muttrc is currently empty, but gets automatically
   filled with the macros to switch between mail accounts, this will
   always appear as a modified file in `git status`. Also when all mail
   accounts get deleted via mutt-wizzard.sh, personal.muttrc gets
   deleted and therefore might cause inconveniences this way.
3. This makes it virtually impossible to accidentally commit personal
   mutt configurations, which would be pretty easy if personal.muttrc
   stays part of this repo as a tracked file.
4. It makes the repo look and feel nicer.

Add new domains to domains.csv

Ask for a login name during account creation

This should resolve #6.

Fix smtp url for manually entered smtp servers

This fixes one half of #6.

Added all domains of gmx.net and zoho.com to domains.csv and fixed error in README.md

This is first working version of an added login query to the account
creation process. It fixes the first part of #6, but there still needs
to be more testing for the second part of that issue, which concerns
creating accounts with domains not listed in domain.csv.

replaced "my" with "by" in two lines

Update domains.csv: add fastmail.com

Domain additions