Define the 'type system' rules for vectors

[vkostyukov]

Since, we want to move out of the factories, we have to provide the explicit set of rules for common operations. This ticket is only about vectors. There idea is to have the table like this:

Operand A	Operand B	Operation	Result Type
DenseVector	DenseVector	any operation	DenseVector like A
DenseVector	double	any operation	DenseVector like A
DenseVector	SparseVector	A + B or A - B	DenseVector like A
SparseVector	DenseVector	A * B	SparseVector like A
SparseVector	SparseVector	A * B	SparseVector like A
SparseVector	SparseVector	A + B or A - B	SparseVector like A
SparseVector	double	A * B or A / B	SparseVector like A
SparseVector	double	A + B or A - B	the default DenseVector

Here like means that the resulting vector should has the same type as A or B. Simple speaking, we should do a.blank() or b.blank() for those cases.