Clear equipment tab for trips display

And prevent the user from editing equipment in trip edit mode (those edits
are both meaningless and of course will be ignored once we save the
changes to the trip).

Also moved some code for setting up tanks, weights, tags, etc, into the
"this is not a trip-edit" part of the updateDiveInfo() function.

Fixes #392

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>