[WIP]: persistent analysis, part I

[MikhailArkhipov]

Closes #1112
Closes #1177
Closes #1178
Closes #1205
Closes #1221

Works in basic scenarios like import sys. Should be merged in inactive state - remove creation of the database service in Server initialization by commenting out

_services.AddService(new ModuleDatabase(_services));

• Introduces 'qualified name' to types. This is how type is identified in the module saved analysis. For example, A.B.C for method C inside method B in class A. i:mod:z is an instance of type z defined in module mod.
• Provides model classes for modules, classes, functions, properties, variables.
• Fixes issues when declaring module for Union and collections from typing was actually builtins.
• Uses LiteDb to save models to file. Currently uses one file per module for convenience of debugging.
• Splits PythonModule to partial classes.
• Provides code to recostruct types from qualified names.
• Implements database service to get module constructed from the db instead of running analysis.

See outstanding issues in the epic on what is not handled yet.