Fix unauthorized access and modification of project data (CVE-2020-15120)

An authenticated member of one project can modify and delete members of
another project, without knowledge of this other project's private
code. This can be further exploited to access all bills of another project
without knowledge of this other project's private code.

With the default configuration, anybody is allowed to create a new
project. An attacker can create a new project and then use it to become
authenticated and exploit this flaw. As such, the exposure is similar to
an unauthenticated attack, because it is trivial to become authenticated.

This issue was caused by a wrong database queries in PersonQuery.

For more details, see https://github.com/spiral-project/ihatemoney/security/advisories/GHSA-67j9-c52g-w2q9

ihatemoney/models.py

@@ -380,7 +380,7 @@ class Person(db.Model):
         def get_by_name(self, name, project):
             return (
                 Person.query.filter(Person.name == name)
-                .filter(Project.id == project.id)
+                .filter(Person.project_id == project.id)
                 .one()
             )
 
@@ -389,7 +389,7 @@ class Person(db.Model):
                 project = g.project
             return (
                 Person.query.filter(Person.id == id)
-                .filter(Project.id == project.id)
+                .filter(Person.project_id == project.id)
                 .one()
             )