Various changes to license ads

1. Relicense config under same license as the rest of the codebase:
   - It's easier.
   - Although it was committed to the public domain, the public domain
     allows for relicensing.
   - The unlicense is controversial.
2. Have branding's README point to the global CC_BY-SA.txt copy.
3. Update README to reflect these changes.

README.md

@@ -47,10 +47,10 @@ bear with me.
 
 ## Licensing
 
-* `main.py`, `RenderUtils.py` and `MiscUtils.py` all use the BSD 3-Clause license. A copy of this license can be
-  found at `/BSD-3-CLAUSE.txt` in the source repository.
-* `config.py` is under the Unlicense. A copy of this license can be found within the file itself.
+* `main.py`, `RenderUtils.py`, `config.py`, and `MiscUtils.py` all use the BSD 3-Clause license. A copy of this license 
+  can be found at `/BSD-3-CLAUSE.txt` in the source repository.
 * Wiki content (under `content` and `images`) is licensed under CC BY-SA. A copy is included at `/CC_BY-SA.txt` on the
   site, and at `/static/CC_BY-SA.txt` in the source repository.
 * Views are licensed under the BSD 3-Clause license. A copy of this license can be found at `/BSD-3-CLAUSE.txt`.
 * Anything under `static` should be assumed to be unlicensed unless specified otherwise.
+* Everything under `/branding` is under CC BY-SA 4.0. A copy of this license can be found at `/CC_BY-SA.txt`.