[Buttons] - Loading state should be customizable in terms of position

[aguscruiz]

As a general rule for buttons, we decided the following:

• Action icons on buttons should generally be on the left side.
• Status icons should be on the right side.

That means that the loading state, with the spinner, should be able to go on either side, depending on where the icon is going to be.

Example:

• If the button has a left side icon, when in loading state, the spinner should be on the left.
• If the button has a right side icon, in loading state should be on the right