[iOS] Update spacing in Settings' TableView

This CL changes the spacing in the Settings. In particular it changes:
- The estimated height for header/footer to avoid some constraints being
  broken.
- The spacing displayed when there is no header/footer in a section.
- The spacing around the link footers.

Bug: 913538
Change-Id: Id634b2dc55ebed3daeffae78168a1f8fa08b4673
Reviewed-on: https://chromium-review.googlesource.com/c/1371388
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616264}
2 files changed