add reusable button component

[ossmate]

Add reusable button component which should let us pass props like:

• onclick
• type
• buttonText
• loading (it should display loader, next to button label)
• className
• rest props

It should also have predefined three types of button:

• default
• primary
• secondary

^ we don't have design system yet, so just prepare the predefined styles colors to something which be easily to change