Viewer: Add a collapsible sidebar for displaying metadata

[lastzero]

As a user, I would like to see additional metadata in a collapsible sidebar so that I don't have to leave the viewer.

Each media type requires different information to be displayed (for example, the dimensions and MP for images, and the codec and duration for videos):

photoprism/pkg/media/types.go

Lines 4 to 13 in 36a359e

	Unknown Type = ""
	Animated Type = "animated"
	Audio Type = "audio"
	Document Type = "document"
	Image Type = "image"
	Raw Type = "raw"
	Sidecar Type = "sidecar"
	Live Type = "live"
	Vector Type = "vector"
	Video Type = "video"

In the first step, the information displayed can be static, containing only the data already available in the viewer (lightbox):

We can make it editable later, e.g. by adding edit buttons, as shown in the example above.

[lastzero]

The above commit adds a proof-of-concept for displaying picture metadata in the viewer sidebar. In the first step, the information displayed can be static, containing only the data that is already available without performing any backend requests. We can later make it editable, for example by adding edit buttons, as shown in the example above.