DEV-13813: Only write SVG symbol definitions to PDF output once

@geealbers good catch, writing these SVGs for each section was an oversight, this should fix it

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DEV-13813

Please briefly describe the goal of this pull request and how it may impact Quire's functionality.

We were including SVG symbol definitions to display CC license icons in PDF output, but they were being included before each <section> element

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Only write SVG symbol definitions for the first collection index

thegetty / quire