BUG Fix the anchor selector to work for internal pages.

Currently it will only default to pulling in anchors from the current
page, from the editor.
Merge pull request #3347 from mateusz/plat-61

Fix the anchor selector to load anchors from other internal pages.
BUG Return the promise instead of the whole deferred object.
Merge pull request #3352 from mateusz/anchor-defer

BUG Return the promise instead of the whole deferred object.
Testing empty absolute urls and more thorough tests