cmake: Fix building when Qt5 is in a non-standard location

The previous method was not providing proper include paths (-I) to the compiler.
Using the qt5_use_modules macro, one can specify both include paths and library
locations at once.

It is also not required to explicitly list all of the dependencies separately;
using just Script and WebKitWidgets works fine.

v2: Add missing QtSql module as per feedback at [1]. Apparently my system has
this set up implicitly while the Emdek's one does not.

[1] https://github.com/Emdek/otter/pull/192#issuecomment-36239973
cmake: building with 2.8.10.2 works just fine