profile: port event unhiding to QtQuick

This has UI changes:
- The unhiding options are accessed by a field that appears when
  there are hidden events.
- Only event-types of this particular dive are unhidden.

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

core/event.h

@@ -64,6 +64,8 @@ public:
 	const struct event *next(); // nullptr -> end
 };
 
+extern bool has_individually_hidden_events(const struct divecomputer *dc);
+
 /* Get gasmixes at increasing timestamps. */
 class gasmix_loop {
 	const struct dive &dive;