Many fixes

...components/gradient_waveforms/changing_gradient_blocks.jl

...components/gradient_waveforms/constant_gradient_blocks.jl

src/components/gradient_waveforms/gradient_waveforms.jl

src/components/gradient_waveforms/no_gradient_blocks.jl

src/components/instant_gradients.jl

src/containers/building_blocks.jl

src/containers/linearise.jl

src/parts/epi_readouts.jl

src/parts/helper_functions.jl

src/parts/slice_select_rephases.jl

src/parts/spoilt_slice_selects.jl

src/parts/trapezoids.jl

src/pathways.jl

src/variables.jl

test/test_post_hoc.jl