MetroWindow will show the Min/Max/Close buttons over Flyouts that are open and have Position=Right, like Github for Windows.
Fixed the behavior for windows with "ShowTitleBar" set to false.
Previously, a double-click anywhere would resize the window.

This fixes #608
Thanks @KevinGerard
Merge pull request #618 from MahApps/notitlebar-fix

Fixed #608
Merge pull request #617 from Amrykid/flyout-system-buttons

Window Buttons overlap Flyouts
That wasn't right...