FIX: Coregistration UI fixes and improvements

[henrikkauppi]

• Fixed the positions of left and right fiducial registration buttons by switching their places so that they now match the layout of the axial slice view.
• Improved the consistency of the button layout in the coregistration panel by moving all the buttons for navigating between different pages to the bottom of the screen and adding a missing "back" button to the TMS coil page. Labels of some buttons were also simplified and changed for consistency.

[rmatsuda]

Thanks for the PR @henrikkauppi. I believe that the Patient registration should have the right and left correspondence with real world. And only the image registration flipped.