refactor error handling part 1 (#307)

- created `getErrorMessage` function which takes in an error string or any type of error object and returns the correct error message
- replaced `error.message` with `getErrorMessage` since `error` could be a string in some cases
- merged sendNotificationForError.ts with ErrorHandlingUtils.ts
- some minor refactoring

In part 2, I will make the following changes:
 - Make `Logger.logError` function take an error message string instead of an error object. This will reduce some redundancy where the `getErrorMessage` function is being called twice (the error object passed by the caller is already an error message).
 - Update every `TelemetryProcessor.traceFailure` call to make sure we pass in an error message instead of an error object since we stringify the data we send.

tsconfig.strict.json

@@ -15,13 +15,11 @@
     "./src/Common/DeleteFeedback.ts",
     "./src/Common/HashMap.ts",
     "./src/Common/HeadersUtility.ts",
-    "./src/Common/Logger.ts",
     "./src/Common/MessageHandler.ts",
     "./src/Common/MongoUtility.ts",
     "./src/Common/ObjectCache.ts",
     "./src/Common/ThemeUtility.ts",
     "./src/Common/UrlUtility.ts",
-    "./src/Common/dataAccess/sendNotificationForError.ts",
     "./src/ConfigContext.ts",
     "./src/Contracts/ActionContracts.ts",
     "./src/Contracts/DataModels.ts",