* Rename "soft ack" to echo
The ack parameter is often confused with what might be called
"hardware ack"
(see https://forum.mysensors.org/post/34263 for one of many
lengthy discussions)
This change should make it harder to confuse echo with the
hardware ack, and reflects more accurately what will actually
happen.
This fixes https://github.com/mysensors/MySensors/issues/1103
I hope I have found all places where the naming needs to be
changed, and that I haven't inadvertently renamed any of the
*real* ack stuff.
Thanks to @tekka007 for reviewing the changes
and catching my mistakes.
