Add DomAttributes property to UIComponent<TOwner>

[YevgeniyShunevych]

Add property to UIComponent<TOwner> and IUIComponent<TOwner>:

public UIComponentDomAttributesProvider<TOwner> DomAttributes { get; }

UIComponentDomAttributesProvider<TOwner> members:

public ValueProvider<string, TOwner> this[string attributeName] { get; }

public ValueProvider<TValue, TOwner> Get<TValue>(string attributeName);

public string GetValue(string attributeName);

public TValue GetValue<TValue>(string attributeName);