CoreShaderManager class added: helps to keep track of active programs
CoreVBO creating and usage has been simplified and corrected

There are now only two methods on the CoreFactory to create CoreVBO:

<T extends Buffer> CoreVBO<T> createVBO(CoreVBO.DataType dataType,
CoreVBO.UsageType usageType, int size);
<T extends Buffer> CoreVBO<T> createVBO(CoreVBO.DataType dataType,
CoreVBO.UsageType usageType, Object[] data);

instead of a lot as there have been before. The new enums
CoreVBO.DataType and CoreVBO.UsageType allows now the specification of
the data type (Float, Short, etc.) that is stored in the buffer and the
usage type (STATIC_DRAW, DYNAMIC_DRAW, STREAM_DRAW) to be specified
directly. Please note that the CoreVBO.DataType also specifies the NIO
Buffer instance the class uses: FLOAT -> FloatBuffer and SHORT ->
ShortBuffer at the moment.