fix #1414. added cf model interface method 'insertionFollowSpeed' which is only used for safety checks at insertion time. The results defaults to the maximum safe speed as used by the default krauss model

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@16946 29f149b2-0c63-11e1-8f5c-a347f6a9acd0