Print plugin issue with layouts with a name longer than 2 chars

[offtherailz]

The layout selector, on change event, split the old layout removing the first 2 chars from the old layout id to create the new id. It works with layouts like A3, A4 and so on, but fails for layouts like LETTER, 11x17 ....

e.g.
A4_2_pages_with_legend --> LETTER_2_pages_with_legend works LETTER_2_pages_with_legend --> ``A4TTER_2_pages_with_legend fails.

references:
https://github.com/geosolutions-it/MapStore/blob/master/mapcomposer/app/static/externals/GeoExt/lib/GeoExt/plugins/PrintProviderField.js#L122

https://github.com/geosolutions-it/MapStore/blob/master/mapcomposer/app/static/externals/PrintPreview/lib/GeoExt.ux/PrintPreview.js#L537

These should be replaced with something like :

         if(currentLayout.indexOf('_2_pages_compact_legend') > 0){
            var index = currentLayout.indexOf('_2_pages_compact_legend');
            currentLayout = currentLayout.substr(0,index);
        } else if(currentLayout.indexOf('_compact_legend') > 0){
            var index = currentLayout.indexOf('_compact_legend');
            currentLayout = currentLayout.substr(0,index);
        } else if(currentLayout.indexOf('_2_pages_legend') > 0){
            var index = currentLayout.indexOf('_2_pages_legend');
            currentLayout = currentLayout.substr(0,index);
        }

[Gnafu]

This issues is still open because the fix ( 6e0f967 ) must be ported on the master branch