Merge pull request #4 from fexbraun/master

Allow string values in Gauges
Health check response details are now visible in the dashboard.

UI changes:
- moved ping column above healthcheck
- added new column 'Details' with all details about the health check

Implementation details:
- Had to change the logic from simple success / error to always return
the JsonNode with the healthcheck information.
- The dashboard JS code is now looking for 'healthy = false' to decide
if a health check was successfull or not.
- introduced a new parent json node healthCheckResponse to have all
health check information under one parent instead of top-level mixed
with other response information.