[Input] Correct the default icon size in input component

[nicmell]

The default icon size in the input should be 16px, it's instead 12px.

The problem is that the icon in the Search component (that inherits from Input) is 12px, and the icon size is not configurable.

Porposed solution:

Allow to pass a ReactElement to the iconBefore and iconAfter prop, allowing to specify the size and the color for the icon.

-<Input iconBefore={PiMagnifyingGlass} />
+<Input iconBefore={<Icon component={PiMagnifyingGlass} size={12}/>} />