records: exposing record metadata revisions

(addresses #1990)

* Extends `get_record` with optional `revision` parameter
* Exposes revision for record information (metadata) tab
* Adds a config variable CFG_RECORD_REVISION_URL_PARAMETER
  with default value of "revision"

Signed-off-by: Bogdan Kulynych <bogdan.kulynych@gmail.com>
Maybe move the new `record` parameter to the end?  Some external sites may rely on the order of parameters of `format_record()` in their overlays.  (Because they existed since ages.)  Adding new parameters at the end, even if not pretty, helps in smoother upgrading.