Fauxton: use .listenTo and not .on

There was no `.off` call on destroy, so these two Eventhandlers
where leaking memory
Fauxton: Extract a common filter component from logs

Create a reusable component from the filter that is used in logs,
that can be used in for tasks like
COUCHDB-2158 ("Apply filter with custom params on changes feed page")
and other situtations where a filter is needed.