Bug 13378: Add a filter to search suggestions not linked to a fund

Bug 13378: Add a filter to search suggestions not linked to a fund

This patch adds a "None" option for the fund filter.

Test plan:
1/ Go on the suggestion search page
2/ Search suggestions not linked to a fund using the "None" option.
3/ Search all suggestions (linked or not to a fund) using the "Any" option.

Works as expected.
Signed-off-by: Marc Veron <veron@veron.ch>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>