policies/expression: migrate to raw python instead of jinja2 (#49)

* policies/expression: migrate to raw python instead of jinja2

* lib/expression: create base evaluator, custom subclass for policies

* core: rewrite propertymappings to use python

* providers/saml: update to new PropertyMappings

* sources/ldap: update to new PropertyMappings

* docs: update docs for new propertymappings

* root: remove jinja2

* root: re-add jinja to lock file as its implicitly required

docs/expressions/reference/user-object.md

@@ -0,0 +1,21 @@
+# Passbook User Object
+
+The User object has the following attributes:
+
+ - `username`: User's Username
+ - `email` User's E-Mail
+ - `name` User's Display Name
+ - `is_staff` Boolean field if user is staff
+ - `is_active` Boolean field if user is active
+ - `date_joined` Date User joined/was created
+ - `password_change_date` Date Password was last changed
+ - `attributes` Dynamic Attributes
+
+## Examples
+
+List all the User's Group Names
+
+```python
+for group in user.groups.all():
+    yield group.name
+```