cmake: move SVM(Linear)Classifier.cpp files into "marsystems" folder
cmake: enlist core source/header files in CMakeLists.txt

Reasons:

1. This is better than listing files in another file, because it allows
"make" to automatically call "cmake" when a file is added to, removed from,
or renamed in the list.

2. I don't imagine anyone contributing to Marsyas core who wouldn't know
how to enter their file at the right place in CMakeLists.txt.