Add new hook WatchlistEditorBeforeFormRender

This will allow subscribers to batch-load everything they
need beforehand, instead of loading everything piecemeal
on a per-line basis when WatchlistEditorBuildRemoveLine
is called.

Change-Id: I362e25b585921d755d6564955ac685971386f29b
Merge "Add new hook WatchlistEditorBeforeFormRender"