refactor: remove frameless window

remove frameless window and merge it into mainwindow. because we do not need frameless and transparent window, so most of its functions are removed in previous commits.

CMakeLists.txt

@@ -39,7 +39,6 @@ endif ()
 
 set (PPIC_CPP_FILES
     app/main.cpp
-    app/framelesswindow.cpp
     app/mainwindow.cpp
     app/actionmanager.cpp
     app/graphicsview.cpp
@@ -57,7 +56,6 @@ set (PPIC_CPP_FILES
 )
 
 set (PPIC_HEADER_FILES
-    app/framelesswindow.h
     app/mainwindow.h
     app/actionmanager.h
     app/graphicsview.h