Changed unittests in corelib to use specific headers instead of super-headers.

Changed unittests in corelib to use specific headers instead of super-headers.

Modified unittests to use specific class headers instead of
using super-headers like QtCore that pull in all the headers for
the module.
- Decreasing build time.

Change-Id: I9c3fd0767be15205893bb406f609c8283a2a3a5a
Reviewed-by: Kurt Korbatits  <kurt.korbatits@nokia.com>
Reviewed-by: Jason McDonald <jason.mcdonald@nokia.com>
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>