Add a new namespace TensorAccessors
Add a new namespace TensorAccessors

This namespace will contain a collection of algorithms working on generic
tensorial objects (of arbitrary rank).

The rationale to implement such functionality in a generic fashion in a
separate namespace is
 - to easy code reusability and therefore avoid code duplication.
 - to have a well-defined interface that allows to exchange the low
   level implementation.

JaeryunYim/dealii,EGP-CIG-REU/dealii,danshapero/dealii,sairajat/dealii,spco/dealii,angelrca/dealii,JaeryunYim/dealii,JaeryunYim/dealii,ESeNonFossiIo/dealii,johntfoster/dealii,EGP-CIG-REU/dealii,shakirbsm/dealii,adamkosik/dealii,nicolacavallini/dealii,andreamola/dealii,gpitton/dealii,ibkim11/dealii,angelrca/dealii,YongYang86/dealii,danshapero/dealii,naliboff/dealii,ESeNonFossiIo/dealii,shakirbsm/dealii,sairajat/dealii,maieneuro/dealii,Arezou-gh/dealii,shakirbsm/dealii,ibkim11/dealii,danshapero/dealii,nicolacavallini/dealii,angelrca/dealii,kalj/dealii,kalj/dealii,andreamola/dealii,naliboff/dealii,pesser/dealii,sairajat/dealii,danshapero/dealii,jperryhouts/dealii,johntfoster/dealii,naliboff/dealii,Arezou-gh/dealii,naliboff/dealii,spco/dealii,EGP-CIG-REU/dealii,Arezou-gh/dealii,pesser/dealii,andreamola/dealii,kalj/dealii,sairajat/dealii,shakirbsm/dealii,kalj/dealii,maieneuro/dealii,Arezou-gh/dealii,maieneuro/dealii,nicolacavallini/dealii,EGP-CIG-REU/dealii,spco/dealii,adamkosik/dealii,spco/dealii,johntfoster/dealii,pesser/dealii,ESeNonFossiIo/dealii,JaeryunYim/dealii,pesser/dealii,andreamola/dealii,andreamola/dealii,pesser/dealii,andreamola/dealii,nicolacavallini/dealii,johntfoster/dealii,Arezou-gh/dealii,kalj/dealii,ESeNonFossiIo/dealii,maieneuro/dealii,nicolacavallini/dealii,spco/dealii,kalj/dealii,adamkosik/dealii,sairajat/dealii,ibkim11/dealii,ibkim11/dealii,Arezou-gh/dealii,shakirbsm/dealii,gpitton/dealii,angelrca/dealii,jperryhouts/dealii,ESeNonFossiIo/dealii,jperryhouts/dealii,ESeNonFossiIo/dealii,YongYang86/dealii,gpitton/dealii,shakirbsm/dealii,pesser/dealii,YongYang86/dealii,johntfoster/dealii,pesser/dealii,gpitton/dealii,jperryhouts/dealii,naliboff/dealii,ibkim11/dealii,EGP-CIG-REU/dealii,gpitton/dealii,jperryhouts/dealii,gpitton/dealii,jperryhouts/dealii,YongYang86/dealii,nicolacavallini/dealii,danshapero/dealii,maieneuro/dealii,naliboff/dealii,andreamola/dealii,adamkosik/dealii,sairajat/dealii,ibkim11/dealii,EGP-CIG-REU/dealii,ibkim11/dealii,YongYang86/dealii,nicolacavallini/dealii,JaeryunYim/dealii,JaeryunYim/dealii,danshapero/dealii,angelrca/dealii,adamkosik/dealii,maieneuro/dealii,naliboff/dealii,YongYang86/dealii,maieneuro/dealii,adamkosik/dealii,shakirbsm/dealii,ESeNonFossiIo/dealii,angelrca/dealii,adamkosik/dealii,EGP-CIG-REU/dealii,kalj/dealii,spco/dealii,johntfoster/dealii,johntfoster/dealii,spco/dealii,jperryhouts/dealii,angelrca/dealii,YongYang86/dealii,gpitton/dealii,sairajat/dealii,Arezou-gh/dealii,danshapero/dealii,JaeryunYim/dealii