[web] Add option to change search modal size

Summary: It should be possible to use small and large modals.

Test Plan: Check existing usages - they should look the same. Render a large modal and check if its size is increased.

Reviewers: benschac, atul, def-au1t

Reviewed By: benschac, atul

Subscribers: ashoat, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3644