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

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

Views creation for all pages needed + css update

do not forget to update dependencies.