[response/v0.7.1.1] modify RESPONSE headers, rather than REQUEST

in addition,
to differentiate this version of the addon (from the original),
the following identifiers have been changed:

* UUIDs:
    * old: b749fc7c-e949-447f-926c-3f4eed6accfe
      new: b3731343-bd49-4146-b6b2-48935ea627e1
    * old: 6b2f2fc7-a26c-4602-a08d-bd6d065a86e3
      new: f76b2347-aea1-483d-861b-06b392bfa38f
    * old: feb80fc3-9e72-4fc5-bc72-986957ada6cc
      new: 1bb30833-e65f-492a-b8eb-9422b69716c7
    * old: 0eff9eeb-c51a-4f07-9823-27bc32fdae13
      new: c5c58352-a576-4c0b-bb27-b4a860c6689f
    * old: 86e57f10-469a-11e0-9207-0800200c9a66
      new: d5f398ce-f73b-4ccc-8601-edbeb4a4d8a9

* contract IDs
    * old: @modifyheaders.mozdev.org/header
      new: @modifyheaders.mozdev.org/response/header
    * old: @modifyheaders.mozdev.org/service
      new: @modifyheaders.mozdev.org/response/service
    * old: @modifyheaders.mozdev.org/proxy
      new: @modifyheaders.mozdev.org/response/proxy
    * old: @mozilla.org/autocomplete/search
      new: @mozilla.org/autocomplete/response/search

* content/locale URIs
    * old: chrome://modifyheaders/
      new: chrome://modify-response-headers/