[Feature] Ability to display transparent tray icon

[XakerTwo]

As noted in #229, when transparent background is enabled, text become jagged (aliased) and this happens due to 1bit mask. However, since WinXP (docs; 2nd approach; comments) tray icons supports transparency(alpha/32bit), so it's possible to solve this issue

There some complications and troubles with using GDI and ClearType(especially ClearType - it's additive and subpixel-alpha-ed) But here is possible solution: calculating of additive alpha and applying it to bitmap manually

Note: this is not perfect solution because calculated alpha is additive, which is not what actual alpha blending expects.

Note: i'm continue to use BITMAPINFOHEADER because ARGB is a default order; if you wish you can switch to BITMAPV5HEADER and init bitmap according to docs (that was initial implementation, so rest of the code would works as is)

This is a cumulative PR, includes #269 #270