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.
Merge pull request #45 from sainsaar/master

Estonian TTS: handled roundabouts for the pedestrian mode