App: add tool meta information (canonical url, rdf/xml, plaintext)

[TimidRobot]

Fixes

• Fixes Add plaintext license link to XHTML versions #317 by @RichardLitt
• Fixes make canonical URIs more visible on the website #361 by @eroux
• Fixes [Feature] add localized markup and styling for canonical url, and formats meta information to deed and legal code page contexts #390 by @possumbilities

Description

App:

• add tool meta information (canonical url, rdf/xml, plaintext)
• improve consistency of title header

Also see Data PRs:

• Data (gettext): add tool meta information (canonical url, rdf/xml, plaintext) cc-legal-tools-data#162
• Data (publish): add tool meta information (canonical url, rdf/xml, plaintext) cc-legal-tools-data#163 (includes screenshots)

Technical details

• Box alignment in flexbox - CSS: Cascading Style Sheets | MDN
• Mastering wrapping of flex items - CSS: Cascading Style Sheets | MDN

Tests

Name    Stmts   Miss Branch BrPart    Cover   Missing
-----------------------------------------------------
TOTAL    1659      0    566      0  100.00%

20 files skipped due to complete coverage.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main or master).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

Developer Certificate of Origin

For the purposes of this DCO, "license" is equivalent to "license or public domain dedication," and "open source license" is equivalent to "open content license or public domain dedication."

Developer Certificate of Origin

Developer Certificate of Origin
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(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
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[possumbilities]

All seems sound. Approved!