Merge remote-tracking branch 'origin/feature/8233_icat_update_external_dl_url'
Removed old ICAT interface classes. Refs #8274.

- Removed relevant classes from cmake list.
Removed advancedSearch from application window. Refs #8274.
Removed MyDataSearch from application window. Refs #8274.
Removed ICatSearch from application window. Refs #8274.
Renamed ICatHelper class. Refs #8274.
Renamed ICatSearch class. Refs #8274.

- Renamed `Login` `search`, and `logout` variables in `ApplicationWindow.cpp` to be ICAT independant.
- Renamed relevant interface class to match related class name.
- Updated CMakeLists.
Merge branch 'feature/8274_icat_remove_old_gui' into develop