Restructure project directories (#333)

`/client/web` -> `/frontend`
`/client/cli` -> *delete for now*
`/client/native` -> *delete for now*
`/core/editor` -> `/editor`
`/core/document` -> `/graphene`
`/core/renderer` -> `/charcoal`
`/core/proc-macro` -> `/proc-macros` *(now plural)*

frontend/src/components/widgets/widgets.ts

@@ -0,0 +1,97 @@
+export type Widgets = TextButtonWidget | IconButtonWidget | SeparatorWidget | PopoverButtonWidget | NumberInputWidget;
+export type WidgetRow = Array<Widgets>;
+export type WidgetLayout = Array<WidgetRow>;
+
+// Text Button
+export interface TextButtonWidget {
+	kind: "TextButton";
+	tooltip?: string;
+	message?: string | object;
+	callback?: Function;
+	props: TextButtonProps;
+}
+
+export interface TextButtonProps {
+	// `action` is used via `IconButtonWidget.callback`
+	label: string;
+	emphasized?: boolean;
+	disabled?: boolean;
+	minWidth?: number;
+	gapAfter?: boolean;
+}
+
+// Icon Button
+export interface IconButtonWidget {
+	kind: "IconButton";
+	tooltip?: string;
+	message?: string | object;
+	callback?: Function;
+	props: IconButtonProps;
+}
+
+export interface IconButtonProps {
+	// `action` is used via `IconButtonWidget.callback`
+	icon: string;
+	size: number;
+	gapAfter?: boolean;
+}
+
+// Popover Button
+export interface PopoverButtonWidget {
+	kind: "PopoverButton";
+	tooltip?: string;
+	callback?: Function;
+	// popover: WidgetLayout;
+	popover: { title: string; text: string }; // TODO: Replace this with a `WidgetLayout` like above for arbitrary layouts
+	props: PopoverButtonProps;
+}
+
+export interface PopoverButtonProps {
+	// `action` is used via `PopoverButtonWidget.callback`
+	icon?: string;
+}
+
+// Number Input
+export interface NumberInputWidget {
+	kind: "NumberInput";
+	tooltip?: string;
+	callback?: Function;
+	props: NumberInputProps;
+}
+
+export interface NumberInputProps {
+	value: number;
+	min?: number;
+	max?: number;
+	step?: number;
+	stepIsMultiplier?: boolean;
+	isInteger?: boolean;
+	unit?: string;
+	unitIsHiddenWhenEditing?: boolean;
+	displayDecimalPlaces?: number;
+	label?: string;
+	disabled?: boolean;
+}
+
+// Separator
+export interface SeparatorWidget {
+	kind: "Separator";
+	props: SeparatorProps;
+}
+
+export interface SeparatorProps {
+	direction?: SeparatorDirection;
+	type?: SeparatorType;
+}
+
+export enum SeparatorDirection {
+	"Horizontal" = "Horizontal",
+	"Vertical" = "Vertical",
+}
+
+export enum SeparatorType {
+	"Related" = "Related",
+	"Unrelated" = "Unrelated",
+	"Section" = "Section",
+	"List" = "List",
+}