Make possible to specify the container element for the viewer

[danxuliu]

The viewer does not set nor allows to set a specific element as the container of the modal dialog, and by default modal dialogs use the body element. However, in some cases the viewer needs to be appended to a different element (for example, if a sub-element is shown in fullscreen mode, like done in Talk), as otherwise it would not be visible.

How to test

• Open a conversation in Talk
• Share a picture in the conversation
• Switch to full screen mode
• Try to open the viewer for the picture

Expected result

The viewer is shown.

Actual result

The viewer is not shown (and neither its overlay).

[ShGKme]

Would it be fine to add a container prop, to pass it to the NcModal's container?

[skjnldsv]

At this point I would like to refactor the Viewer and make it a package alongside this app :see_no_evil: So people can import and call the Viewer