Estonian TTS: handled roundabouts for the pedestrian mode

Previously, the Estonian TTS said "sõitke ringristmikule" meaning
"ride/drive to the roundabout". This was incorrect for the pedestrian mode.
Now it says "kõndige" ("walk") instead of "sõitke", if the appMode is
'pedestrian'. For other modes the saying is unchanged.

For many roundabouts there is actually a walkway apart from the exits,
but for some there isn't. Thus, in those cases there is probably no way
to reroute the pedestrians apart from just saying the exit as we already do.