change data model and migration script

(start working on #18)

(unique fields are automatically indexed in Django)

disease rows are now unique and managed with a manytomany field
fixes #19

from PPI, CompoundAction, TestActivityDescription
fixes #37

fixes #24

- separate Ppi into Ppi and PpiComplex classes (fixes #36)
- replace ActivityType table with an enumerated type
- remove complex from foreign keys when not required

closes #35

further progress requires to answer question asked in #36

(closes #9)

Add Wizard form functionalities to generate successive forms & update css according to the new forms.

Update Django admin page and Admin session. Create forms needed and update css file for forms elements

- remove petitjean properties
- canonical smile is 500 chars long everywhere

do not forget to update dependencies.

(fix #11, fix #23)

correct Domain model, use PFAM service, add migration command
and update database.