- CLean up: Separate models and interfaces

- API to get a value given a key
- API to update value smartly
- Fine grained configuration change event
- Smart reload API
- Remove unnecessary APIs

This reverts commit 838d4a33.

- Provide folder specific keys

* Fix more Compiler Errors for TS 2.4 in the VSCode codebase

* Fix compile error for 2.3

- language
- resource

- Refactor configuration services to read settings from multiple folders
- Implement merging strategy for multi root workspace settings
- Implement a configuration model that can be reused across layers
- Implement getRoot API in workspace context service

- Use '[...identifiers]` as key

- Contirbute parsing of config as an option to config watcher
- Introduce Config model to hold configurations , overrides and necessary data for services
- Refactor config services to use config models
- Add an api in config services to get configuration for a language

This reverts commit 1dbf76bf.