Support for multi-root .code-workspace workspaces

[award999]

• Support workspace folder variable subsitution, ex. ${workspaceFolder:proj1}
• When a code-workspace add the configured name instead of the relative path as a postfix to the task name
• Add same postfixes to plugin tasks
• For Run and Debug Build commands, all fetching launch configurations from outside the workspace
• Add a new test target to test a handful of currated suites to make sure that .code-workspace support does not break

Issue: #1072