Moved window classes and adjusted references

Moved the browse and import window into the gui/windows folder

ArtNet/artnet_manager.py

@@ -10,8 +10,8 @@ from PyQt5.QtWidgets import QApplication
 from ArtNet.db.db_adapter import DBAdapter
 from ArtNet.file.file_reader import FileReader
 from ArtNet.file.config_reader import ConfigReader
-from ArtNet.gui.importer_window import ImporterWindow
-from ArtNet.gui.browse_window import BrowseWindow
+from ArtNet.gui.windows.importer_window import ImporterWindow
+from ArtNet.gui.windows.browse_window import BrowseWindow
 from ArtNet.gui.dialogs.db_connection_dialog.db_dialog import DBDialog
 from ArtNet.web.link_generator import LinkGenerator
 from ArtNet.singleton_manager import SingletonManager