This commit syncs msmtp-scripts with master as current
openwrt-19.07 is broken.

Cherry-picks and squashes the following commits from
master.

6d8cff9a msmtp-scripts: Fix LICENSE information
d163eaea msmtp-scripts: Overhaul and update like upstream
3c15d410 msmtp-scripts: Make conn_test default nc
b9cc3cf2 msmtp-scripts: Fix spool/lock dir permissions
f76408af msmtp-scripts: Add msmtprc permission docs

Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>