Support storage layer for storing entities and relationship

[shivasurya]

Is your feature request related to a problem? Please describe.
To scale for small -> medium level codebase (1000s of declared methods, classes) it is essential to have some storage layer such as sqlite, postgres to reduce memory pressure, have efficient queries, lazy loading of entities and effective filtering use of #190 class and inheritance.

Describe the solution you'd like
sqlite or postgresql might be perfect fit instead of storing it in memory + figure out relationship using foreign key

Describe alternatives you've considered
Datalog like fact storage

Use case
What will this feature enable for you?

1. Scale for small -> medium level codebases (1000s of methods, classes, interface etc)
2. effective filtering using class support and thus reduction in search space while executing query

Additional context
N/A