Update libceed version to the one required for building MFEM4.7

[sshiraiwa]

• MFEM4.7 requires libceed 0.12.
• Removed Python3.7 from the list of release.
• Update version number to 4.7.0rc1

[justinlaughlin]

👍

[sshiraiwa]

Merging this, since it fixed the most of issues