Windows port

[roman-yagodin]

WPF Backend lacks number of features:

• It cannot load SVG images. I think we should convert icons we use to PNG on build (e.g. with inkscape -z -e test.png test.svg), or implement SVG loading via external library.
• It doesn't have StatusIcon implementation. Could be simulated with taskbar - minimize on close, and close app via Exit command in the main menu. Update: cannot minimize window via Xwt, as its look like a window manager responsibility.

Can expect number of issues with clipboard.

Also, assemblies for supported backends should not be referenced in the project file directly, but we still need to copy required files into output directory on build - see #2, #5.

[roman-yagodin]

Windows port is working, but will require testing after each release.

Probably it's better to provide two releases - one with most recent changes for Linux and not-so recent, but manually tested one for Windows. This can be achieved by adding some kind of note to release version like "R7.Webmate.X.Y.Z-wintested"