mediawiki.jqueryMsg: Extend mw.Message with new #parseDom method

mediawiki.jqueryMsg: Extend mw.Message with new #parseDom method

Unlike #parse, this one returns a jQuery set of DOM nodes and not a
HTML string, for two benefits:

* Allows to skip unnecessary HTML serialization and reconstruction
  when we just want to insert the message contents somewhere.

  Old way:
    $( '#foo' ).html( mw.message( 'foo' ).parse() );
  New way:
    $( '#foo' ).append( mw.message( 'foo' ).parseDom() );

  This is roughly equivalent to the old alternative:
    $( '#foo' ).msg( 'foo' );
  But that way can't be used if you start with a mw.Message object, or
  don't yet know where the elements will be inserted.

* Allows to preserve the event handlers when a function is passed as
  message parameter.

    mw.messages.set( 'foo', '[$1 Click me!]' );
    $( '#foo' ).append( mw.message( 'foo', function () {
      console.log( 'Link clicked!' );
    } ).parseDom() );

Change-Id: Ia09131c2ffc1d149ca6b1c32dcd918a539c3a719