Several compiler warnings with MSVC++ #254
Description
When compiling sgpp with MSVC++, several warnings pop up that might indicate unintended behaviour:
\base\src\sgpp\base\grid\storage\hashmap\HashGridPoint.hpp(376,72): warning C4146: unary minus operator applied to unsigned type, result still unsigned
\base\src\sgpp\base\grid\storage\hashmap\HashGridPoint.hpp(398,72): warning C4146: unary minus operator applied to unsigned type, result still unsigned
\base\src\sgpp\base\grid\storage\hashmap\HashGridPoint.hpp(426,71): warning C4146: unary minus operator applied to unsigned type, result still unsigned
\base\src\sgpp\base\grid\common\IndexInSubspaceGenerator.hpp(51,23): warning C4834: discarding return value of function with 'nodiscard' attribute
\base\src\sgpp\base\operation\hash\common\basis\PolyBasis.hpp(167,24): warning C4334: '<<': result of 32-bit shift implicitly converted to 64 bits (was 64-bit shift intended?)
\base\src\sgpp\base\operation\hash\common\basis\BsplineBasis.hpp(1645,1): warning C4334: '<<': result of 32-bit shift implicitly converted to 64 bits (was 64-bit shift intended?)