Add support for multi root workspaces with the new language server server

[DonJayamanne]

Based on #1149

Solution - Start multiple language clients one for each work space

Requirements:

• Lazy load language clients (based on active workspace folder), i.e. don't open for each folder unnecessarily
• Shutdown language client when a workspace folder is removed

[DonJayamanne]

activateWorkspace of src/client/activation/activationManager.ts