CRUD for operation terms

[jgaehring]

Taxonomy terms for operations (ie, not the specific tasks, but the SOP used in each task) can still only be created and modified by importing board data. Provide a UI for adding, editing and deleting locations.

As with crops (#4), these have an associated color attribute, which is currently displayed in the FlowBoardOperations component:

farm-flow-board/src/components/FlowBoardOperations.vue

Lines 10 to 15 in 8c4a0d0

	<span v-for="(op, i) in operations" :key="i">
	<svg viewBox="0 0 24 24" width="24" height="24" xmlns="http://www.w3.org/2000/svg">
	<circle cx="12" cy="12" r="12" :fill="op.color"/>
	</svg>
	&nbsp;{{op.name}}
	</span>

The colors here are selected to correspond with the magnets currently being used in the physical whiteboard, so it's best to stick to this palette, but it will be nice to give users control over these in the future.