Webkit2.

Adding documentation and cleaning how signals are arranged to place
relevant signals next to each other, to have a better understanding
on how these relate to each other in respect to webkit1 and webkit2.

Change-Id: I8badc56d8d95c66d5b5b90433f39a30e7ba53609
Signed-off-by: Leo Ufimtsev <lufimtse@redhat.com>