specfem workshop fixes

[bch0w]

Just a list of bugfixes or clean up tasks for items that cropped up during or after the SPECFEM Users Workshop (10-05-22) that should be addressed at some point:

• Day 1A set major and minor X-axis tick labels on the record section
• Any day: MPI runs with >1 processor may fail for single core machines (like old Macbooks), especially when running SPECFEM3D (this is fine, most modern machines can handle this)
• ! rm command may sometimes return a 'shell-init: error retrieving current directory' (This is fine, doesn't break workflow)
• Fix misfit equation Day 2a Section 4a, should be s(t) - d(t)
• Add Day 2C notebook (Aakash looking at Liu, Tromp kernels)
• Day 2B update velocity model incorrect Vp value
• Day 2B Section 2B don't time reverse adjoint source

[bch0w]

The above issues were addressed in ea5e69c and 6bf0c4b