Introduce a 'skip' attribute for APIs that use the skip pattern.

Some backend's use a 'skip' attribute instead of a 'page' attribute
where the value of 'skip' represents the number of elements to skip in
the current collection. It should be a multiple of the 'iip' attribute.
Simplify resolving the baseUrl by using Underscore.

This piece of code essentially duplicates what _.result does so just use
that instead.