oxarticlelist::loadIds -> optionally preserve the ordering of articles

When retrieving a result list of article ids from external sources (Solr, etc. ) and afterwards you want to create a list of oxarticles via the oxarticlelist, you lose the ordering. oxArticleList::loadIds will return a list where the occurance of the articles is random (it depends on what ids the database finds first). 
Since the ordering is important, especially when using score algorithms based on tokens, hit counts in different fields or stemming, one wants to preserve it.
I've added an optional parameter to allow this. It is backwards compatible and shouldn't do any harm to other modules.