fix animated background image processing

[ubertao]

Fixes animated QR code feature.

Existing code has several issues:
line 184: extra frame when extend()'ing bg_images[] list
line 199: same references of qr_img copy in res_images[]
line 227: duration parameter misspelled as uration

[heuer]

Thanks!

The bug in line 227 was introduced by mistake in 5ffe6d7