The "index.php" in page URLS should be hidden

[rht]

For how to do this: https://www.mediawiki.org/wiki/Manual:Short_URL. This also means that we should:

• start using non-empty $wgScriptPath
• remove hard-coded dependencies on checking if the string index.php is present in the URL (this is currently the case with the page title detection). Ideally we want a semantic way to obtain the page title