Relion 1.4 Subtomogram averaging

For sub-tomogram averaging, which was implemented with help from Tanmay Bharat, a former postdoc in the Lowe group at MRC-LMB, the same holds as for helical processing. Many general concepts remain the same as for single-particle analysis, and users intending to perform sub-tomogram averaging in relion are encouraged to go through this tutorial first. For a detailed description of the sub-tomogram averaging procedures, the user is referred to the corresponding pages on the :textsc:`relion Wiki`, or to Tanmay’s paper[BRL+15]. Please note that we are still actively working on making the sub-tomogram averaging pipeline more convenient to use and better. This work is done in close collaboration with the group of John Briggs, also at MRC-LMB. Meanwhile, please be advised that the sub-tomogram averaging pipeline is considerably less stream-lined than the single-particle one, and users should be prepared to do some scripting outside the relion pipeline for many cases.