Modernize timer example
Modernize timer example

  - Destructure tabris import to make the code more compact and to avoid
    using the global tabris object.
  - Use let instead of var.
  - Prefer lambda functions over anonymous functions.
  - Inline MARGIN constants, since they may introduce unnecessary
    complexity in the scope of examples and snippets where layouts
    don't have to be exchangeable and the variable name is much longer
    than the primitive number itself.

Change-Id: Id00f2452464380a166d3fe4efb87a43ce3ac2339

eclipsesource/tabris-js,eclipsesource/tabris-js,eclipsesource/tabris-js