Usual mix of incremental features and small fixes.
- Allow Tabs to be hidden or disabled dynamically from a ui_control msg.
- Finally remove deprecated second output from ui_chart node.
- Allow ui_form to be submitted with empty fields (if they are not required)
- Don't try to close non-existent menu at start (logging issue only) - Issue #470
- Add startsWith polyfill for IE11
- Ensure active sidebar menu item is highlighted - Issue #472
- Sanitise display of html input - Issue #473
- Respect msg.socketid to return msg back to selected session when using ui_template
- Allow dropdown to have 0 pre-configured values, by removing validation.