Add tests for instantiating cursor delegates in the Loading state.

Components created by QML are usually (always?) ready when assigned to
n property, but it possible for an externally supplied component to
still be loading, as in the test and the code handles it.

Change-Id: I2058e3479e2e711b52af2a0128e6e4c4c3ff7504
Reviewed-by: Martin Jones <martin.jones@nokia.com>