1. new logic to assign category
Step 1 - look for category provided inside the mail body, using the
         special keywords defined by Tesi.
         mantis_begin
         categoria=CATEGORY NAME,  IMPORTANT ',' is mandatory
         assignto=user email,
         mantis_end

Step 2 - If Step 1 fails:
         look for category with name defined in DEFAULT_CATEGORY_NAME
         inside the project where we are trying to create the issue.
Step 3 - if Step 2 fails, then use category defined in plugin configuration

2. Possibility to assign issue on creation using special keyword (assignto)
   mantis_begin
   categoria=CATEGORY NAME,  IMPORTANT ',' is mandatory
   assignto=user email,
   mantis_end

3. On mail created automatically to comunicate user. issue creation the TEXT part
   of original body is added AFTER the standard Tesi message.