Use Catch for our test suite

`make check` is also added to compile and run the tests
Catch is fetched with cmake automatically into the build directory when needed

tests/uuid.cpp

@@ -0,0 +1,13 @@
+#include "catch.hpp"
+
+#include <xmpp/xmpp_component.hpp>
+
+TEST_CASE("id generation")
+{
+  const std::string first_uuid = XmppComponent::next_id();
+  const std::string second_uuid = XmppComponent::next_id();
+
+  CHECK(first_uuid.size() == 36);
+  CHECK(second_uuid.size() == 36);
+  CHECK(first_uuid != second_uuid);
+}