vty: Document some previously undocumented parameters

Katerina pointed out that some nodes are not fully documented and
proposed some messages. The token/timeout messages were correct, I
have modified the other messages. I removed the full-stop from the
PING/PONG documentation as we are normally not using a full sentence.
doc: Do not have examples with accept-all in our repository

We do not want to tell random users to run a network with the
accept-all. This was pointed out by Katerina.
bsc: Stop "show paging" from crashing before the first paging

The paging structure is still initialized lazily and we attempt
to traverse it before it is ready. The crash was discovered by
Katerina. Removing the lazy initialization will take a bit of work
as the gsm_data_shared is used by the osmo-bts and the OpenBSC but
paging is different.