Add PD Application Banners

[molly-moen]

Description

Add banners to homepage and https://code.org/educate/professional-learning/middle-high that notify teachers that applications are open:
homepage:

/middle-high if teacher is not nominated:

/middle-high if teacher is nominated:

homepage on mobile size:

middle-high on mobile size:

Links

• spec
• jira

Testing story

Validated banners look correct on different sizes and browsers.

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[agealy]

Thanks for moving quickly and separating these out into their own PR! Let's just make sure they don't go out before Monday's DTP

[islemaster]

Looks great!