Change minesweeper to extend scene.vwf instead of navscene.vwf

Refs #3015
Fix mine synchronization issue when a second client joins after the first has started the game

Refs #3137
Fix start button synchronization

Refs #743
Merge pull request #113 from virtual-world-framework/branch/fix-minesweeper-bugs

Branch/fix minesweeper bugs

Fixes #743, #3137