ECMS-5521: [IE8] Problem on Display image in Thumbnail view on Insert content link

Problem analysis:
	- In Thumbnail View, there are 8 contents per page but the current code only treats 6 contents per page.
	- In IE 8, children does not work well in Content Selector.
	- Iterator in List View does not work well.

Fix description:
	- Correct that there are 8 contents per page  for thubnail view
	- Replace children function by find function
	- Correct iterator for list view to avoid duplicating result.

Conflicts:
	apps/resources-wcm/src/main/webapp/javascript/eXo/wcm/frontoffice/private/ContentSelector.js