Object: `on` and `once` methods now accept target argument.
View: Fixed binding event handlers.
View: Comment out export symbols.
.gitignore: Ignored .idea folder.
View: Added appendView method.

Appends a new view into this view's element as a child.
Utils: Concat only strings in concatString method.
View: Added setAttribute, getAttribute and removeAttribute wrappers.
Button: Added disable, enable and toggle methods.
Object: Reverted optional target for event binding.

We should always bind events to View object and also listen them for DOM elements too.
View: Bind events to class itself.

Minor code refactor for using transposed EventTypes map.
View: Override Object::on to support two way binding for DOM events.
View: Override Object::off to remove events binded to DOM element.
View: Override Object::once to support two way binding for DOM events.
Build: Compiler fixes.
Bootstrapper: Added button sample.
Index: Fixed compiled.js path on compiled/index.html.
Merge branch 'master' of github.com:fatihacet/spark