User manual: add text for the dive planner

Text for the dive planner has been added to the user manual.
This includes two new images.

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

This patch adds text and figures to the user manual, explaining how to
add photographs to the dive profile.

A 2-sentence paragraph was added to the dive planner text, detailing
planning for repetitive dives.

Signed-off-by: Willem Ferguson <willemferguson@zoology.up.ac.za>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
User manual: add more about dive log export.

This patch updates the information about dive log export.
Export to Worldmap, as well as to HTML are covered.

Small typo corrections elsewhere in the manual.

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