Widget control design

**Problem:** Making view names, messages, classes and selectors configurable for more flexibility can lead to a lot of options to handle. CanJS currently doesn't allow deep extension of defaults.
## Option 1: A separate name for each option

How to handle a large number of options?

```
{
headerSelector : 'header',
bodySelector : 'body',
overlayClass : 'modal-overlay',
title : 'A dialog',
initView : '//my/widget/init.ejs'
}
```
## Option 2: Deep extension

CanUI extends can.Control to do allow deep extension of defaults:

```
{
select : {
header : 'header',
body : '.body'
},
classes : {
overlay : 'modal-overlay'
},
view : {
initView : '//my/widget/init.ejs'
}
title : 'A dialog',
}
```
## Option 3: Configuration object

Provide a configuration object for settings that deal with widget customization:

```
{
config : new can.ui.Configuration({
select : {
header : 'header',
body : '.body'
},
classes : {
overlay : 'modal-overlay'
},
view : {
initView : '//my/widget/init.ejs'
}
}),
title : 'A dialog',
}
```

Start by reviewing the current CanJS can.Control behavior and how CanUI handles widget defaults. Compare the three configuration approaches described in the issue, then establish and implement one agreed design for configurable view names, messages, classes, and selectors; done means the chosen API supports those customizations consistently.

Written by the indexing model from the issue text.