Two-tone Win10 option improvements

[bonzibudd]

The next release will have some visual changes to the Two-tone style:

• Wider drop shadow radius (using GIMP editor) to match Windows 10 exactly
• Better smoothing around corners (limited by Open-Shell and Aero transparency)
• Slightly wider curve radius

Here's what it looks like, although the changes are only subtle.

The main functional difference is the support for automatic colorization with immersive colors.

[bonzibudd]

Addressed #95 in release 1.4.