refactor: use UI file for main window

- main window now use UI file for layout.
- remove all manual computed widget position code. use full Qt layout implementation instead.
- remove useless functions in main window
- change style changed slot as private

CMakeLists.txt

@@ -78,6 +78,7 @@ set (PPIC_UI_FILES
     app/settingsdialog.ui
     app/aboutdialog.ui
     app/metadatadialog.ui
+    app/mainwindow.ui
 )
 
 set (PPIC_QRC_FILES
@@ -119,6 +120,11 @@ else()
     qt_add_translations(${EXE_NAME} ${ADD_TRANSLATIONS_ADDITIONAL_ARGS} TS_FILES ${PPIC_TS_FILES} QM_FILES_OUTPUT_VARIABLE PPIC_QM_FILES)
 endif()
 
+# YYC MARK:
+# This is essential, otherwise Qt UIC generated UI header file
+# can not find our header files if there are custom widgets inside UI file.
+target_include_directories(${EXE_NAME} PRIVATE app/)
+
 target_sources(${EXE_NAME} PRIVATE ${PPIC_QM_FILES})
 
 target_link_libraries (${EXE_NAME} Qt${QT_VERSION_MAJOR}::Widgets Qt${QT_VERSION_MAJOR}::Svg Qt${QT_VERSION_MAJOR}::SvgWidgets)