Language fallback from sh (Serbo-Croatian) to bs, sr-el, hr

Language fallback from sh (Serbo-Croatian) to bs, sr-el, hr

Bosnian, Serbian and Croatian are closely related languages and have
respectively about 2700, 1400 and 1200 translations identical to that
of Serbo-Croatian, which has about 5400 in total. This demonstrates
that we can profitably reuse some translators' work to reduce the
usage of English in Serbo-Croatian despite the low level of translation
and that there is a logical order in the fallback sequence.

The information has been collected and discussed with translators at
https://translatewiki.net/wiki/Thread:Portal_talk:Sh/Language_fallback
and Wikipedia editors have been notified of the discussion with
https://sh.wikipedia.org/w/index.php?diff=40677113&oldid=40676567
and messages in the talk page of each individual editor.

Inherit linktrail and digit separators, but not $defaultDateFormat,
$datePreferences, $datePreferenceMigrationMap or
$namespaceGenderAliases to reduce the impact and variance.

Change-Id: I04310ee32370ae20c00ea970b3163dcb8f167eba