Feature/helmholtz

Introduction of a Helmholtz tutorial to introduce users to elliptic solvers. 

See merge request !10

Made tutorial files so they would compile and added in cmake configuration formatting so it can be executed from any directory

Updates so that tutorial cpp files do not compile directly. Slightly modified code output and put in first (non working) attempt at a regression test

Updated MeshConvert references to NekMesh and also added in an ARCHIVE option to the cylinder case since this seemed to be missing

Updated paths to be consistent with web page layout for download of .tar.gz (Also a few minor editsion in teh advection-diffusion tutorials)

Added missing tst file.



See merge request !9

Feature/adr tutorial

This tutorial added in a basic introduction to using the ADRSolver and running an Advection-Diffusion problem. This is to setup in a new basics directory and contains some regression tests.  

See merge request !8