1d set/getindex for abstract sparse

ref #7023

This implements `setindex!` and `getindex` with 1d and boolean indices for `AbstractSparseMatrix`. An optimized implementation for `SparseMatrixCSC` can be done separately.
There is a difference in performance. Here's a code snippet and some results for comparison: https://gist.github.com/tanmaykm/6871d2d014df4a92f40f

But it does not seem significant.