Update of user manual

Several updates are implemented here.

1) Updates to the dive planner section, following excellent
suggestions from Rob.

2) Updates reflecting the date picker, including hitting ESC
to close the calendar.

3) The edit of device names.

4) Several small or typographic edits

Signed-off-by: Willem Ferguson <willemferguson@zoology.up.ac.za>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>