Remove border from toolbar in default theme
PlatformWindow class for raising and pasting to a window
Allow to set stylesheet for main window
Start working on tests for OS X.
Merge branch 'master' of https://github.com/hluk/CopyQ into mac-support

Conflicts:
	src/gui/mainwindow.cpp
Updates to mac platform code.

- move all code for foreground/background switches into
  ForegroundBackgroundFilter
- move window code out of macplatform into macplatformwindow
- get rid of static m_currentPasteWindow
- greatly simplify getting current window
- send "Cmd-V" using dispatch_after, and ensure that the paste event
  goes to the intended window.
- greatly simplify window logic