- make use of traits
- short array
- better implementation of query findByPk

"Item" parameter keys are the values of the checkbox list,
while the values are the checkbox labels.

for consistency with GridViews DataColumn where the same property is
also named format

avoid XSS with emails in format  "Carsten Brandt <mail@cebe.cc>"

fixes #1261

fixes #1244

fixes #1246

code style section has been added here:
https://github.com/yiisoft/yii2/wiki/Core-framework-code-style#self-vs-static

verification code for properties:
https://gist.github.com/cebe/7566916

issue #1246

also made everything conistent with client validation

this allows to be able to call error action.

fixes #1244

fixes #1220

```map``` and ```indexOf``` on arrays were only added in IE9.
Changed to make use of jQuery's equivalents.