Make qvec always a vector and qval dependent on whether orientation is fixed

src/MRIBuilder.jl

src/all_building_blocks/base_building_blocks.jl

src/all_building_blocks/spoilt_slice_selects.jl

src/all_building_blocks/trapezoids.jl

...components/gradient_waveforms/changing_gradient_blocks.jl

...components/gradient_waveforms/constant_gradient_blocks.jl

src/components/instant_gradients.jl

src/pathways.jl

src/variables.jl