Export format selection

[mbarto]

We need to implement a configurable plugin for the Printing dialog that will:

• allow the user to choose an export format between the ones advertised by the mapfish engine, eventually restricted by configuration (configuration option)
• show a (localized) label to describe the control (configuration option)
• store the chosen format in a custom spec property (configuration option)
• implement an alternative viewer for image files to show / download them (the actual viewer is for PDF files only)

This is a very generic plugin, so can be added to the MapStore core codebase.

Note: formats must be enabled in the yaml layout file, to add more formats than the standard PDF.
A simple way to enable all the supported formats is to add this to the config.yaml file:

formats:
  - '*'

[mbarto]

Depends on geosolutions-it/MapStore2#7652

[mbarto]

Waiting for geosolutions-it/MapStore2#7682 approval