Replace Newsmatch 2019 CTA on homepage with INN Days 2020 CTA

[benlk]

For https://github.com/INN/umbrella-inndev/issues/141

Note for future devs: $ convert 74865172-59d8fc80-5316-11ea-9b03-c5bb04229d36.JPG -resize 2000x2000 74865172-59d8fc80-5316-11ea-9b03-c5bb04229d36_2000.JPG

Changes

• Replaces the Texas Tribune image and its smaller sizes with the image from https://github.com/INN/umbrella-inndev/issues/141 and generated smaller sizes
• Replaces the "INN Days 2019" headline with "INN Days 2020", which is what I assume this is for
• Replaces the existing message with "Bringing the brightest nonprofit newsrooms together for intensive business training, June 16 and 17"
• Replaces the link with https://inn.org/inn-days-2020/
• Placeholder text for updated image credit
• Placeholder text for updated photo alt text

Why

Requested in https://github.com/INN/umbrella-inndev/issues/141

Questions

• [x] What is the photo alt text? Please fill in the blanks in:

  Photograph of TKTK PERSON speaking at TKTK EVENT on TKTK DATE about TKTK TOPIC. Photo by TKTK PHOTOGRAPHER for TKTK ORG.

• [x] What is the photo credit? Please fill in the blanks in:

  Photo by TKTK PHOTOGRAPHER for TKTK ORG.

• [x] Is "INN Days 2020" the correct headline?

[benlk]

Next steps:

• [x] answers for questions
• [x] update placeholders
• [ ] create branch in INN/umbrella-inndev and deploy to staging
• [ ] review, merge, deploy.
• [ ] ¿Create issue template for future updates of the homepage?

[MirandaEcho]

Photo credit was on Photo Shelter, which I should have linked. caption/alt text can be taken from this as well.

"INN Days 2019 in Houston June 12, 2019. (Photo by Michael Stravato)"

link: https://inn.photoshelter.com/gallery-image/INN-Days-2019/G000000kzG6oDpAo/I00007o0MLaUqtKI/C0000Dq2AeWO0Wqw

[benlk]

Wording has been updated in https://github.com/INN/inn/pull/121/commits/310b49f0f0045fc27b3587ac7a685c05e643487a. Thank you!