Increase SpinW CI coverage

[rebeccafair]

Before this can be started, the following must be completed:

• Port CI from SpinW4 repository #73

The files which should be tested are (in order of importance)

• spinw.spinw Add unit tests for spinw creation #84, More additions to spinw.m tests #88
• spinw.add* [addaniso, addatom, addcoupling, addmatrix, addtwin] Add unit tests for addX methods of spinw class #85
• spinw.gencoupling Add unit tests for gencoupling #89
• spinw.genlattice Add test for genlattice #99
• spinw.genmagstr Test genmagstr #97
• spinw.optmagk Test optmagk #111
• spinw.optmagsteep Add unit tests optmagsteep #108
• spinw.optmagstr Add optmagstr tests #117
• spinw.spinwave Test spinwave.m #92
• spinw.intmatrix Add unit tests intmatrix #110
• spinw.field Add tests for field #100
• spinw.magstr
• spinw.atom - covered by other tests (e.g. addcoupling)
• spinw.matom - covered by other tests (e.g. addcoupling)
• spinw.basisvector - covered by other tests (e.g. gencoupling)
• spinw.energy
• spinw.getmatrix
• spinw.setmatrix
• spinw.powspec
• spinw.notwin
• spinw.twinq
• spinw.table
• spinw.fourier
• spinw.fouriersym
• spinw.struct - used only by .copy which is covered by other tests (e.g. spinwave, optmag*)
• spinw.symop

Some files outside the SpinW class should also be tested (in order of importance):

• sw_egrid @rebeccafair
• sw_neutron
• sw_instrument
• sw_qscan
• sw_rot
• sw_model

The following files should be tested but are part of the Horace interface so may need Horace (or a mock-up of Horace):

• spinw.horace covered by pace-integration
• spinw.horace_sqw covered by pace-integration
• spinw.matparser covered by pace-integration

The following is the plotting - I'm not sure how to test it without rewriting it in an MVP architecture...

• spinw.plot
• sw_plotspec