MBS-2021: Derive recording.length from median(track.length)

Introduces a new 'median' aggregate for PostgreSQL and subsequently uses
it to calculate the recording.length column from all tracks linked to that
recording.
MBS-2021: Add upgrade scripts
MBS-2021: Do not allow updates to recording lengths that are not standalone
MBS-2021: PgProve the new recording.length properties
MBS-2021: Regenerate SQL scripts
MBS-2021: Fix tests since the schema change
Ignore recording length edits in the RE and elsewhere
Delete recordings from cache when tracks are inserted/updated/removed

These actions may cause the recording length to change.
Clear recordings from cache after TOC is attached
Pass used_by_tracks to recording create form
Merge branch 'beta' into mbs-2021
Factor out median_track_length function, fix pgTAP tests
Update update script
Remove memcached from Perl dependencies section because it's realdy installed in the Prerequisites section
Add libicu-dev to Perl Prerequisites section
Merge pull request #98 from tylerlong/master

Remove memcached from Perl dependencies section because it's realdy inst...
Merge branch 'beta'

* beta: (43 commits)
  MBS-7432 again: another ISE displaying user tags page
  Fix qunit failure introduced by 3bd1a5a
  Fix WHERE-clause test for table-specification change.
  MBS-7432: beta: Internal server error displaying user tags page
  MBS-7297: Internal server error when searching for edits by ID with large numbers
  MBS-7315: Removing URL entity via Edit Release page results in SQL error
  mbs-7425: add maniadb to the whitelist
  MBS-7420: Can't submit artist edit form after adding and removing a URL
  MBS-7431: URL encoding problem with inline URL editing
  MBS-7429: table-qualify the edit search ID predicate with BETWEEN, like with other predicates and operators
  MBS-7428: beta: error when adding new releases with DiscID
  mbs-7426: removing extra N
  MBS-7417: Mark recording length mismatch in release merge
  Factor out checking for length differences
  delete now-worthless release group deletion test
  MBS-7416: Beta: edit-medium diff shows recording changes that aren't actually changes
  MBS-7291: Highlight large length spread in merge
  Move artist/recordings-list.tt to components/
  MBS-7412: Beta: reorder medium edits are generated for new releases
  MBS-7153: Show artist credits on tag pages
  ...
Merge remote-tracking branch 'bitmap/mbs-2021'

* bitmap/mbs-2021:
  Update update script
  Factor out median_track_length function, fix pgTAP tests
  Pass used_by_tracks to recording create form
  Clear recordings from cache after TOC is attached
  Delete recordings from cache when tracks are inserted/updated/removed
  Ignore recording length edits in the RE and elsewhere
  MBS-2021: Fix tests since the schema change
  MBS-2021: Regenerate SQL scripts
  MBS-2021: PgProve the new recording.length properties
  MBS-2021: Do not allow updates to recording lengths that are not standalone
  MBS-2021: Add upgrade scripts
  MBS-2021: Derive recording.length from median(track.length)
Hopefully fix test failures by properly using $1 rather than recording_id in SQL function definitions
Fix recording UUID in Recording::Edit test.