[x] Implemented Base Window Class for all further windows
[x] Improved and fixed frameless resize helper
[x] Use new TitleBar class in MainWindow
[x] Use FlowLayout in MainWindow
[x] Rewrite BrowserWindow
[x] Add customizable URL interceptor to new BrowserWindow, remove hardcodes
[x] Don't create/delete BrowserWindow instances in MainWindow still in the MainWindow, but duplicate code was removed and the instance creation reduced to 1 line
Don't create/delete BrowserWindow instances in MainWindowstill in the MainWindow, but duplicate code was removed and the instance creation reduced to 1 line