Add `autoShow` option

This commit adds an `autoShow` option which pops up the suggestion
list (if appropriate) when the input element is focused.

Change-Id: I82a8da58455147d6c873aa936786ee12f469f50d
Reviewed-on: https://gerrit.causes.com/19121
Reviewed-by: Tony Wooster <tony.wooster@causes.com>
Tested-by: Tony Wooster <tony.wooster@causes.com>