Fix specfile serious bug: qmlscene not installed

To run cool-old-term Qt5's qmlscene binary is required. The specfile, however, did not have QtDeclarative-devel as requirement specified.

I also made some adjustments to the BuildRequirements as "pkgconfig" is the recommended cross-distro way, hopefully enabling building cool-old-term under Mageia 5.
Merge pull request #102 from KAMiKAZOW/patch-7

Fix specfile serious bug: missing dependency