Gh369 clone repository

#369 
see code from:
https://github.com/flower-platform/flower-platform-3/blob/master/org.flowerplatform.web.git/src/org/flowerplatform/web/git/GitService.java

clone command must be executed in a job because there are problems if 2 users are trying to clone in the same time

if something happens and repo isn't cloned entirely, the downloaded data must be deleted.