Update markup of templates to Bootstrap 5

[santonelli]

Due to #2967 we have to update icons and markup of the templates listed below. Feel free to add missing templates here.

• plone.app.mosaic.browser.templates.layouts-editor.pt

[santonelli]

@balavec Is this basically done? The only template i found in this package has not been touched since 5 years. Fell free to close this issue.

[balavec]

Hey @santonelli I will look into this. Thank you for the heads up.