BO36 - Create a page to list all the Sponsors for a Sponsorship level

[gregoriopalama]

Create a page that will use the BackOfficeLayout.
The page should be opened by clicking on the name of a Sponsorship level, in the page created in #189.

The page's layout should be as following:

The page will list all the Sponsors and show their name and logo. For each sponsor, the page will provide the link to edit and to delete the single sponsor. Also, we will provide a button to move the sponsor down and one to move the level up. In this issue, these buttons won't be implemented, but only added graphically.

The breadcrumb should provide the navigation to the sponsorship levels' list.
A searchbar in the top of the list will allow to filter the sponsors by their name. The filter must be client side.
A button on the right of the searchbar will allow to add a new sponsor.

Depends on #123, #189 and #181.