Biggie: introduce libamarokshared.so library to avoid building things in shared/ twice

Shared libraries exist to *cough* share built code, use them! This is first part
of much larger buildsystem changes planned in Randa 2012.

This also brings some other changes that were needed, namely avoiding UTILITIES_BUILD.
From changes to top-level CMakeLists.txt it may look as if kdelibs are now needed even
when just utilities (not player) are built. This was however the case for at least a
year now. To be able to build utilities w/put kdelibs we'd need:
 a) require newer CMake to do automoc for us
 b) replace KDE's KMimeType by Qt5's QMimeDatabase

Static member s_fileTypeStrings of FileTypeSupport is not used outside
the FileType.cpp -> make it a plain static compilation unit variable to
prevent problems with static variables shared across multiple shared
libraries.

@Patrick: this needs at least build testing on Windows to ensure I've done the
KDE_IMPORT/EXPORT macros right.

CCMAIL: amarok-devel@kde.org
CCMAIL: Patrick von Reth <vonreth@kde.org>