Use data attributes instead of classes for binding

[brunschgi]

To provide more flexibility we are going to change the naming conventions.
Instead of using classes – .mod .mod-xyz – we will switch to data attributes.

This makes the binding completely independent from styling, so that TerrificJS is compatible with all CSS modularization «philosophies» (e.g. BEM, Atomic Design etc.).

[brunschgi]

The new naming conventions will be:

• .mod .mod-foo => data-t-name="foo"
• .mod .mod-foo skin-foo-bar => data-t-name="foo" data-t-skin="bar"
• data-connectors="overview" => the current connector stuff will be replaced with a more standard EventEmitter