divelog: turn owning-pointers into unique_ptr<>s

Since everything is C++ now, we can use unique_ptr<>s. This makes
the code significantly shorter, because we can now use the default
move constructor and assignment operators.

This has a semantic change when std::move()-ing the divelog:
now not the contents of the tables are moved, but the pointers.
That is, the moved-from object now has no more tables and
must not be used anymore. This made it necessary to replace
std::move()s by std::swap()s. In that regard, the old code was
in principle broken: it used moved-from objects, which may work
but usually doesn't.

This commit adds a myriad of .get() function calls where the code
expects a C-style pointer. The plan is to remove virtually all of
them, when we move free-standing functions into the class it acts
on. Or, replace C-style pointers by references where we don't support
NULL.

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

core/device.cpp

@@ -140,7 +140,7 @@ int is_default_dive_computer_device(const char *name)
 
 const char *get_dc_nickname(const struct divecomputer *dc)
 {
-	const device *existNode = get_device_for_dc(divelog.devices, dc);
+	const device *existNode = get_device_for_dc(divelog.devices.get(), dc);
 
 	if (existNode && !existNode->nickName.empty())
 		return existNode->nickName.c_str();