Add variant_sequential_view class

[acki-m]

Similar to the variant_associative_view class, add a new class called variant_sequential_view.
The variant_array_view class should be marked as deprecated.
The advantage of the new class will be:

• can be easily used in range based for loop
• less member functions, but same functionality
• no internal dynamic memory allocation, when iterator is big enough
• easier internal code to maintain