Assuming you're actively using Nova Launcher:
1. Long-press any empty part of the homescreen, then tap Widgets.
2. Under Nova Launcher (which is probably the first one listed), drag and drop the Activities widget to the homescreen.
3. Now scroll down to Settings and tap it to get more selections. Scroll down further and select Devices (the one that says "bluetooth.BluetoothSettings" in fine print).
4. You should now have a widget on your homescreen that, when tapped, will launch the main Settings>Bluetooth menu.