mediawiki: improve storeConfiguration & loadConfiguration methods

* Use enhanced for-loops (storeConfiguration & loadConfiguration)
* Use curly braces to reduce the variable scope and, to reuse variable names (storeConfiguration)
* Avoid map.get(key) in iterations over each map's entry (storeConfiguration):
      for (Map.Entry<String, Object> entry : ht.entrySet())

Change-Id: I678d5a9f205efb2c89ab868b59e1b654419381d8
Reviewed-on: https://gerrit.libreoffice.org/11331
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>