Refactor initializers

[mikhailChelbaev]

Revise the initializers following these guidelines:

• If a component can be configured with an initial model value, provide it with a default value.
• If a view model includes properties crucial for a component's full appearance, avoid assigning a default model value.

For instance, a button requires the title parameter in the model to be set for it to appear complete, so no default value is provided. Conversely, a loader appears satisfactory with an initial model value, so a default value is provided.