Restores "LegacyWindow" class into a working state

[aik099]

Problems solved:

• the given window handle wasn't used in the Selenium URL building
• when the current meta-handle (only usable for .../position and .../size calls) was used, then LegacyWindow::getHandle was returning it as-is without converting to a real window handle

Closes #138

P.S. Strange Selenium 3 server (maybe Selenium 2 is also affected) behavior I've noticed during testing:

1. both .../position and .../size URLs are returning/accepting array with these keys: x, y, width, height (while they should only use either x and y or width and height
2. both .../position and .../size URLs are operating on the current window regardless if the window handle of another non-active window is specified

I guess, that's a bug in Selenium server itself and not this library.

[aik099]

@robocoder , pleas review.

[aik099]

@robocoder , please review.