Samplesheets Vue app unit test improvements

[mikkonie]

Stuff left over from #750, because I wanted to wrap up that mega issue and continue with more pressing stuff to finalize the v0.9 milestone.

Tasks

• [ ] Set up global warning suppression
• [ ] Add extra editing tests after implementing #1036
• [ ] Test AgGridDragSelect?
• [ ] Solutions for bootstrap-vue testing issues? (see #1030 and #1034)
• [ ] Set up coverage checking for both Python & Vue.js?

[mikkonie]

Tests will have to be reworked for #994 anyway, so this should be done for the new version once rewritten.