In PyQt5.6, connect() does strict checking of the signal signature
against the Slot decorator types, so "@slot(object)" is not a catch-all
anymore.

git grep '<class>' | awk -F : '{print $1}' | while read name; do sed -i 's/<class>/ &/' $name ; done

This is a cleaner approach that requires less configuration
in other applications.
This also easily allows us to have another color.

Many checks were made on being exactly at the DEBUG level, they were
fixed to also check on being below DEBUG (i.e. DEBUG_FILTERS).

python modernize.py --no-six -f libmodernize.fixes.fix_print -w

With manual fixes as the import was put always on top.

Remove useless trailing \
Remove trailing spaces
Add missing empty lines

autopep8 -ir -j2 --select=E301,E302,E502,W291,W293,W391 .

Diff quickly checked.

This is recommended by Debian.
closes #618

While this changes constants names, I think it is important as "accused" is
complely wrong. E-mails use the term "Read-receipts" so I chose
to go with RECEIVED.