Add documentation from core modules

docs/ref/core/01_checks.rst

+Checks
+======
+
+.. automodule:: aleksis.core.checks
+        :members:

docs/ref/core/02_managers.rst

+Managers
+========
+
+.. automodule:: aleksis.core.managers
+   :members:
\ No newline at end of file

docs/ref/core/03_mixins.rst

+Mixins
+======
+
+.. automodule:: aleksis.core.mixins
+   :members:
\ No newline at end of file

docs/ref/core/05_registries.rst

+Core preference registries
+==========================
+
+.. automodule:: aleksis.core.registries
+   :members:
\ No newline at end of file

docs/ref/core/06_search_indexes.rst

+Search indexes
+==============
+
+.. automodule:: aleksis.core.search_indexes
+        :members:

docs/ref/core/07_tables.rst

+Core tables
+===========
+
+.. automodule:: aleksis.core.tables
+        :members:
\ No newline at end of file

docs/ref/core/08_tasks.rst

+Core Celery tasks
+=================
+
+.. automodule:: aleksis.core.tasks
+        :members:

docs/ref/core/09_utils.rst

+Core utillity functions
+=======================
+
+
+General helper functions in core
+---------------------------------
+    .. automodule:: aleksis.core.util.core_helpers
+        :members:
+
+Predicates for permission systemd
+---------------------------------
+.. automodule:: aleksis.core.util.predicates
+        :members:
+
+Messages
+--------
+.. automodule:: aleksis.core.util.messages
+        :members:
+
+General helper functions for models
+-----------------------------------
+.. automodule:: aleksis.core.util.model_helpers
+        :members:
+
+Helper functions for SASS
+-------------------------
+.. automodule:: aleksis.core.util.sass_helpers
+        :members:
+
+Utillity function for AlekSIS app container
+-------------------------------------------
+.. automodule:: aleksis.core.util.apps
+        :members:
+
+AlekSIS core middlewares
+------------------------
+.. automodule:: aleksis.core.util.middlewares
+        :members:
+
+Search utillity
+------------------------
+.. automodule:: aleksis.core.util.search
+        :members:
+

docs/ref/core/10_views.rst

+Core views
+==========
+
+.. automodule:: aleksis.core.views
+   :members: