Move to vue-material-design-icons

Signed-off-by: Julius Härtl <jus@bitgrid.net>

src/components/navigation/AppNavigationBoardCategory.vue

@@ -28,6 +28,9 @@
 		:allow-collapse="collapsible"
 		:open="opened">
 		<AppNavigationBoard v-for="board in boardsSorted" :key="board.id" :board="board" />
+		<template #icon>
+			<slot name="icon" />
+		</template>
 	</AppNavigationItem>
 </template>