Fix `isSelectable` interaction with `click` event

`isSelectable` wasn't being checked on click-selection of a suggestion
element, meaning that unselectable things were being selected. This
commit fixes that bug by checking `isSelectable` in the `select`
method.

Change-Id: I8e55e24c56f33ff532b0bf5e82ff8e44a778a9e0
Reviewed-on: https://gerrit.causes.com/19295
Reviewed-by: Tony Wooster <tony.wooster@causes.com>
Tested-by: Tony Wooster <tony.wooster@causes.com>