Add a specialised lender select.

I’ve used checkboxes as it displays all of the
lenders on the screen, which should make it easier
to view and select lenders. Later on it should make
it more intuitive when we add the “All” option.
Add “All” option when selecting Lenders in LoanReport.
Add jQuery “select all” functionality for instant feedback.
Use a multiple select box, instead of a list of checkboxes to filter by
lender on the Loan Report.
Merge pull request #252 from alphagov/filter-loan-report-by-all-lenders

Filter Loan Report by All Lenders