Revert "Removed Node temporary migrations"

This reverts commit bfcdddb3461afc1075381fbdad8641997f2e51e8.
Layer: removed zoom field #181
Layer: renamed minimum_distance for consistency #181

Renamed minimum_distance in nodes_minimum_distance
Layer: organization field can be blank #181
Layer model indentation improved #181
Layer: reorganized extended node validation #181
Layer: converted area field in GeometryField #181
Layer: ensure area can be only Polygon or Point #181
Layer: replaced center field with a property #181
Layer area cannot be null #181
Added HSTORE_SCHEMA feature to Layer #181
Reorganized documentation images #126
Added layers docs #181 #126