Refactoring the ListingsGridFragment.

- Start using Item instead of Media for the data in the ListingsGridFragment.
- Ordering item by Ascending updated date, so that the newer items show up first.
- Added a primaryMedia column for an Item. This will contain the mediaId for the Primay Media for this Item.
  primaryMedia is single media to be shown in list fragments.
improved detail view
Refactoring the ListingsGridFragment.

- Start using Item instead of Media for the data in the ListingsGridFragment.
- Ordering item by Ascending updated date, so that the newer items show up first.
- Added a primaryMedia column for an Item. This will contain the mediaId for the Primay Media for this Item.
  primaryMedia is single media to be shown in list fragments.
Merge branch 'refactor_listing_fragment' of https://github.com/Hawk-It/HawkItAndroidApp into refactor_listing_fragment
Merge pull request #20 from Hawk-It/refactor_listing_fragment

Refactor listing fragment