fix(viewer): improve styling and loading/error handling

[ShGKme]

☑️ Resolves

• Media is sometimes cut on the bottom
• On slow connection there is just an empty modal
• No error handling

🚧 Tasks

• refactor(viewer): make viewer initialized async
  • required to use @nextcloud/files with @nextcloud/router because it uses router on module init, which is not ready until Talk Desktop is ready
• refactor(viewer): move path utils to a module
• fix(viewer): media is cut on the bottom sometimes
  • NcModal styles in fullscreen has hardcoded position and it wasn't correctly changed to support window title bar
• fix(viewer): add loading and error handling with improved UI
  • Add some new universal components for viewer
    • Base - to display content/loading/error
    • Media - specifically for media to handle media loading and styles

🖼️ Screenshots

🏚️ Before	🏡 After
Small and large Windows	.
Error	.
Slow connection	.

Notes about loading

On fast connection there is no spinner to not blink. It only appears after --animation-slow delay.

Video is also shown once it's ready to be played.

Slow	Fast

[Antreesy]

Looks nice and smooth now =)

[ShGKme]

Thanks @DorraJaouad and @Antreesy, I forgot to test on the light theme 🌕

Fixed, see the last commit

[DorraJaouad]

Tested 🦅 🦅

[ShGKme]

Squashed