Remove unused navigation link
Cleanup
Move value conversion index to separate file in proxy subdirectory

Update test implementation accordingly
Add simple cached Index proxy

- Cached refers to the fact that the deletions are not made directly
  on the index but are cached separately and can be applied later.
- The view on the index is still consistent due to filtering of the
  lookup results.
- Merge, split, subtract, map etc. functions trigger the cache
  to be merged with the index.