Allow secondary tool windows to be maximized

[bttelle]

The window style of secondary tool windows (that get created when you drag a pane outside of the main window) doesn't allow the window to be maximized. Manually sizing the pane gets old and also there is no way to get rid of the thick border on the sides if the window is not maximized.

There is a minimal fix for this in #890 that lets you access it from the title bar popup menu.

Alternate ways of fixing this are:

• add Mazimize style and remove the Toolwindow style that inhibits the standard minimize/maximize buttons; then you don't need to right click
• render custom buttons in the tool window title bar area to allow for a more custom window appearance

I propose accepting my PR for now and then maybe going the custom title bar route as time permits.

[bttelle]

815af77 added support to right-click and select maximize from the titlebar menu. With this flag Windows also lets you maximize by double-clicking the titlebar, dragging the window to the top of a screen or using Window-key Up.