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>
81: D400 First line should end with '.', not 't'
87: D400 First line should end with '.', not 's'
89:5: F401 'get_record_revision_timestamps' imported but unused
90:46: E127 continuation line over-indented for visual indent
91:46: E127 continuation line over-indented for visual indent
93:66: E502 the backslash is redundant between brackets
94:9: E128 continuation line under-indented for visual indent
95:60: E502 the backslash is redundant between brackets
96:9: E128 continuation line under-indented for visual indent