Use new spacing helpers

[BernardZhao]

Since Bulma 0.9 spacing helpers have been added, so my old code where I have been doing spacing myself should use these now and moving forward we should try to take advantage of this as well.

For example, a new spacing helper looks like: <... class="mt-1"> for margin-top of 0.25 rem. Obsolete spacing sets custom margin properties not using this.