Resolve Issues with Header and Footer Embeds

If users added plain text that included special characters to the header embed, a toastr error (syntax err) would be thrown on the buyer page. And if users added any non script tags in the footer, it would break the page -- not show the page content and not allow users to click on any links on the app.

To resolve this, plain text AND plain text with special characters/symbols are no longer supported in the footer or header. Also, <script> tags are the only tags supported in the footer embeds.

If there's an existing issue with the header or footer embeds, they won't be appended to the head/body on the buyer page. Instead, the errors will be logged in the console. With that being said, the page should load with the correct content, not see the syntax toastr error, and function properly (e.g users are able to click on other links on the app if the footer has non script tags)

Additional changes to help users understand what is supported in the embeds:

• Added tooltips next to the header and footer embeds with text describing what is supported in each embed
• Added a REMINDER text in the Embeds tab to remind users that the header and footer embeds are used for any tags needed for third party integrations