hange to 2.5.2 compatibility

Related to #15 ; I'm not a ruby developper but with dirty copy and paste (from redmine project 2.5.2) on issue edit template i now can post note on issue. So, there is my modification in this pull request. Naturally some modification should be done in this copy&pasted code !
Thank's for your addon ;)

Note: Maybe Pull #12 is larger better than mine !!