profile: make event hiding persistent across change of dive

Currently, the "hide event" status is lost when switching dives.
Save it in the event struct instead to make it persistent.

In the future we might save this information to the log file.
Then this should be integrated in the undo-system.

This commit also makes the "unhide events" menu entry more
fine grained: It now differentiates between individual
events and event types.

Note this adds an additional field to the event structure.
There is a "deleted" field that is used internally for
book-keeping, but probably should be removed. Not touching
this at the moment as long as this is C-only code. When/if
switching to C++ we can make the event linked list a table,
which will make this much simpler.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/string-format.cpp

@@ -1,6 +1,7 @@
 #include "string-format.h"
 #include "dive.h"
 #include "divesite.h"
+#include "event.h"
 #include "format.h"
 #include "qthelper.h"
 #include "subsurface-string.h"