visual bug when using translucent window and frosted glass simultaneously

[bellebasso]

following #28, add support for frosted glass and translucency simultaneous usage.

expected behavior:

• add frosted glass borders
• keep the translucency aspect intact (including color and intensity)

current stage:

• add frosted glass borders
• the color of certain ui elements are affected:
  • ribbon
  • note panel

[bellebasso]

implemented in 9d2d837. still in a quite fragile state, lots of random visual bugs.