add subtitles for video feature

add this code to Videos.vue : template->video support many subtitle
`		<track
			:src="davPath.replace(/\.[^\.]+$/, '.en.vtt')"
			label="English"
			kind="captions"
			srclang="en-us" />

		<track
			:src="davPath.replace(/\.[^\.]+$/, '.vi.vtt')"
			label="Vietnamess"
			kind="captions"
			srclang="vi-vn" default />`