Layout Sections

[MGatner]

This PR adds two additional sections to the main app layout: headerAssets and footerAssets. This makes it easier for individual pages to supply their own code that deviates from the rest of the template.

[coveralls]

Pull Request Test Coverage Report for Build 913184274

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 75.938%

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Totals
Change from base Build 864105391:	0.0%
Covered Lines:	243
Relevant Lines:	320

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💛 - Coveralls

[MGatner]

This allows individual pages to add sections, like this:

<?= $this->section('footerAssets') ?>
<style>
header {
    background-color: white;
}
</style>
<?= $this->endSection() ?>