Modernize reddit example
Modernize reddit example

  - Destructure tabris import to make the code more compact and to
    avoid using the global tabris object.
  - 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: I781833b52d8b1ded6c63d81200fb73102196f993

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