As admin I want to delete image from the series

[php-coder]

We should allow to admin to remove image(s) from the series. All except the last one.

Probably, we also should allow the same to the series owner.

Idea from: @AleksSPb

[php-coder]

Don't forget to modify series.updated_at field.

[cssru]

Also don't forget to modify series.updated_by field.

[php-coder]

This will be useful because it also allows to replace an image.