Wrote (so far ignored) planning ITs for index hints in Ronja

Fixes bug in semantic check of index hint clauses
Add hints to query graph
Make index leaf planners plan index hints
Add pretty printing of index hints to query graph and ast doc builders
Make CandidateList prefer plans that use index hints (many hints trumps lesser hints)
Move acceptance tests for index hints to Ronja
License
Adding scan hints to Ronja
Add test for using hints when planning expands
Ensure plans based on index hints are not pruned away too early
Merge pull request #2519 from boggle/index-hints

Index hints