- Create a simple workspace context service for standalone editor
- Use the test context service for tests

From: https://github.com/Microsoft/TypeScript/issues/15352

TS 2.3.1 introduced a breaking change by [switching to covariant types for callbacks](https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#covariance-in-callback-parameters). This change tries to fix these compiler errors in the workbench codebase

- 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