Allow paste multiple watermarks

[Koc]

Q	A
Bug Report?	no
Feature Request?	yes
BC Break Report?	no
RFC?	no
Imagine Bundle Version	latest

For now it is impossible insert multiple watermarks because filter name is key of the array.

[peter-gribanov]

You can solve this problem by creating a additional filter

services:
    liip_imagine.filter.loader.watermark2:
        parent: 'liip_imagine.filter.loader.watermark'
        tags:
            - { name: liip_imagine.filter.loader, loader: 'watermark2' }

and apply it

liip_imagine:
    filter_sets:
        my_watermark_filter:
            filters:
                watermark:
                    image: '../assets/images/watermark1.png'
                    position: 'topleft'
                watermark2:
                    image: '../assets/images/watermark2.png'
                    position: 'bottomright'

But this does not eliminate need to resolve the problem.

[dbu]

seems fixed in #1281