Add support to specify default display options from within the block

[valdisiljuconoks]

"Is it possible to set the default DisplayOption for Block from inside the Block model, like you can do with the Additional Styles? It would be handy when migrating from another renderer with DisplayOption already set into Block."

Q: what do you think - who would win if you are dropping block with display option (DO1) set via attribute, having also override in method (DO2) into the content area with default display option set to DO3?

A: Tough one. The most inner/specific setting (DO2) should be the winner?

[valdisiljuconoks]

@kmukku there is a private build available. wanna try to see whether this solves your issue?