[v1.04] housekeeping

previously:
* the addon that fully supports user-defined javascript
  (and is evaluated using `eval()`)
  was isolated to the repo `moz-rewrite`
* the addon that only supports user-defined JSON
  was isolated to the repo `moz-rewrite-amo`

now:
* the addon that fully supports user-defined javascript
  (and is evaluated using `eval()`)
  has been migrated to the branch `js/eval/master`
  of the repo `moz-rewrite`
* the addon that only supports user-defined JSON
  has been migrated to the branch `json/master`
  of the repo `moz-rewrite`.
  * the repo `moz-rewrite-amo` has been deprecated
* a new addon that fully supports user-defined javascript
  (and is evaluated using `Cu.evalInSandbox()`)
  has been added to the branch `js/Cu.evalInSandbox/master`
  of the repo `moz-rewrite`

see:
* tagged release `json/v1.04` attachement: `changelog.sh`
* this shell script summarizes the key points of this migration process

in terms of necessary housekeeping for `json/master`:
* the following needed adjustment:
  * namespacing-
    * name of the addon (to differentiate it from other variations)
    * name of preferences branch
    * name of resource/content URLs
    * contract id of component
    * placeholder/suggested file paths to input files
  * filenames
  * URLs in copyright comment blocks