Add CSS grid to schedule teasers

[Brian-Clement]

Description

The existing schedule in the style guide did not include any "imperfect" examples of data (i.e. missing speaker images, company logos), and as a result the text was not vertically aligned in cases of content mismatches:

To address this, this PR does the following:

• Removes speaker photo and logo from one row to create a visual example of incomplete content
• Introduces a basic CSS grid with some flex for .schedule__teaser content to align items and vertically center
• Incidentally this also updates composer.json to resolve a JsonValidationException whereby the string "true" was throwing errors upon a composer install.

The output now looks like this:

Desktop

Mobile