Bug 865207 - Move webapps actor from /b2g/chrome/content to /toolkit/devtools/apps/. r=fabrice, r=dcamp

--HG--
rename : dom/apps/tests/unit/data/app.zip => toolkit/devtools/apps/tests/unit/data/app.zip
rename : dom/apps/tests/unit/test_webappsActor.js => toolkit/devtools/apps/tests/unit/test_webappsActor.js
rename : b2g/chrome/content/dbg-webapps-actors.js => toolkit/devtools/server/actors/webapps.js