Migrations for dimensions manager

The dimensions tree has migrations defined for all manager versions that have existed in our code; only a few of these migrations were actually implemented.

StaticDimensionRecordStorageManager 6.0.0 to 6.0.1

Migration script: 1601d5973bf8.py

Adds indices to few skypix overlap tables to accelerate queries.

StaticDimensionRecordStorageManager 6.0.1 to 6.0.2

Migration script: 035dcf13ef18.py

Adds NOT NULL constraints to identifying foreign key columns.