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>
590:42: E231 missing whitespace after ','
590:44: E231 missing whitespace after ','
603:17: E127 continuation line over-indented for visual indent
603:48: E228 missing whitespace around modulo operator
633:26: E128 continuation line under-indented for visual indent