Add support for 'secondary' type for button

[Sakul Budhathoki]

I got warning when used cancelBtnBsStyle="secondary"

Warning Reference:

But It works pretty fine, Reference:

[Daniel Jorgensen]

thanks. i will fix this.

[Valentin]

Maybe change confirmBtnBsStyle, cancelBtnBsStyle to string so any class can be used?
Ok there is cancelBtnCssClass. Still add secondary to the PropTypes.oneOf

[Daniel Jorgensen]

the upcoming 5.0 release will allow any string as the button BS style