move $wgValueParsers to repo

only used by wbparsevalue api module in repo

also, if you happen to explicitly require/load the
WikibaseLib.php entry point before loading repo (Wikibase.php),
then $wgValueParsers gets reset to array() and things break.

The way we check

if ( !defined( 'WBL_VERSION' ) ) {
  @include_once( __DIR__ . '/../lib/WikibaseLib.php' ); 
}
 
in repo indicates it *might* be okay or allowed to explicitly
require WikibaseLib.php before repo.  It is not okay
with how $wgValueParsers was defined.

This makes things work in such situation, and anyway
lib has no use for the global.

Change-Id: I131ab938fb3ff21f9d1108aaf3bfeccc4a584297
Merge "move $wgValueParsers to repo"