Fixed expression templates

Brief summary:

- fixed `DistributedExpressionTemplates`
- many fixes and simplifications in `ExpressionTemplates` and `StaticExpressionTemplates`
- extended tests (unified for `VectorExpressions`, `VectorViewExpressions`, `StaticVectorExpressions`, `DistributedVectorExpressions`, `DistributedVectorViewExpressions`)
- functions `maxNorm`, `l1Norm` and `l2Norm` - convenient aliases for `max(abs(...))`, `lpNorm(..., 1)` and `lpNorm(..., 2)`
- a `cast` function which makes something like this possible:
  `float s = TNL::sum(cast<float>(vector))`, where vector elements may be `int`, `double`, etc.
- fixed result types in expression templates and vertical operations
- removed `addVector`, `addVectors`, `addElement`, `scalarProduct` and `sum` methods from all vector types


See merge request !36

Fixes #41

This allows to easily change the type of elements in a vector
expression, which can be useful to force a specific type when combining
vectors with different element types. For example, a double-vector can
be cast to float to avoid expensive computations in double precision.

Split ExpressionL1Norm, ExpressionL2Norm from ExpressionLpNorm because they have different result type

Also fixed the result types and starting values for other vertical operations.

It is very slow and unnecessary - the user can easily use operator[] or
getElement and setElement for any operation with a single element, not
just addition.

Distributed argMin and argMax are not implemented yet, all other
operations successfully pass all tests (which were unified with the
tests for Vector, VectorView and StaticVector).

Simplified expression templates: pow implemented as a binary expression rather than a special unary expression

Does not work yet for the distributed vector...