portability, video, and more features

Many features, including contributions from Christof Rath (@nobecutan), incrementing on his v0.5.

Portability: bringing pympress up to speed on all platforms

• various look & feel improvements on Mac
• screensaver and video support on Windows
• fixed segfault on Linux, apparently due to non-thread-safe interactions between xlib and gtk/gdk

New features:

• displaying text annotations
• estimated talk time
• stable support for video through a VLC plugin (requires VLC of the same bit-ness as python, it 32 bits or 64 bits)

Other improvements:

• setup scripts now use entry points and uniquely defined version number
• separate options (fullscreen, etc) from startup options in two menus next to each other
• various bugfixes