- 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

* Use the extension descriptions available in the UI thread
* Don't wait for handling extension points until extension host is running
* Create the extension host process only after extension points have been handled
* Send the initial configuration as part of the initData to the extension host

This reverts commit 83053afc.

Revert "added ability to resolve varaibles in configuration settings (variables such as ${workspaceRoot} and ${env...} environment variables"

This reverts commit 9baff519.

added ability to resolve varaibles in configuration settings (variables such as ${workspaceRoot} and ${env...} environment variables