Filter images in JFormFieldImageList

Filter attribute has to be set before field is setup. Otherwise filter would not be used and there are all files from folder in a drop-down
Update imagelist.php

Corrected mistake
Update imagelist.php
Updating installation lang files: af-ZA, bs-BA, pl-PL
Copyright
Merge pull request #2830 from piotrmocko/patch-11

Filter images in JFormFieldImageList
Updating installation lang files: lv-LV