XAFORUM-118 : Remove custom styling for buttons

This is not correct. 
.buttonwrapper is from old Colibri. It's used in combination with class .button. 
.btn is from Bootstrap. It's used in combination with another class like .btn-default. 

Choose one way or another, not a mix of them. If you want to work on Colibri, pick the first solution, since Flamingo extends the .btn rules for the .buttonwrapper structure.