Add a sb_all target and sb_$framework targets to make it easier to build frameworks standalone

Review Request #113506 - Created Oct. 30, 2013 and submitted - Latest diff uploaded

Aurélien Gâteau
buildsystem, kdeframeworks
neundorf, skelly
This patch rework superbuild to integrate it more closely with kdelibs build system: one no longer needs to run cmake path/to/kdelibs/superbuild separately. Instead targets are created for all frameworks declared in superbuild/CMakeLists.txt. For example to build and install ki18n standalone, one can run `make sb_ki18n`. It also adds a special "sb_all" target, which builds and install all standalone frameworks.
kdelibs still builds standalone, all sb_* targets work as expected.