Allow ControlGroups and ControlArrays to contain errors from their level, and
errors from their children. [Design Doc](https://docs.google.com/document/d/1EnJ3-_iFpVKFz1ifN1LkXSGQ7h3A72OQGry2g8eo7IA/edit?pli=1#heading=h.j53rt81eegm4)
BREAKING CHANGE: errors format has changed from validators. Now errors from
a control or an array's children are prefixed with 'controls' while errors
from the object itself are left at the root level.
Example:
Given a Control group as follows:
var group = new ControlGroup({
login: new Control("", required),
password: new Control("", required),
passwordConfirm: new Control("", required)
});
Before:
group.errors
{
login: {required: true},
password: {required: true},
passwordConfirm: {required: true},
}
After:
group.errors
{
controls: {
login: {required: true},
password: {required: true},
passwordConfirm: {required: true},
}
}