simdarray: casts from simdmaskarray to AVX::Mask

I used simd_cast to implement the conversions and had to move the
constructor implementation to avx/simd_cast.h for this to compile.

I also moved some of the public typedefs and traits to avx/types.h.

Also the Vector member type of simdmaskarray was missing.

refs #613

Signed-off-by: Matthias Kretz <kretz@kde.org>
remove dead code

Signed-off-by: Matthias Kretz <kretz@kde.org>
reorder and mark for refactor

refs #605

Signed-off-by: Matthias Kretz <kretz@kde.org>