Bug 1375463 - Move contextmenu related tests into browser/base/content/test/contextMenu. r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D21916

--HG--
rename : browser/base/content/test/general/browser_contextmenu.js => browser/base/content/test/contextMenu/browser_contextmenu.js
rename : browser/base/content/test/general/browser_contextmenu_childprocess.js => browser/base/content/test/contextMenu/browser_contextmenu_childprocess.js
rename : browser/base/content/test/general/browser_contextmenu_input.js => browser/base/content/test/contextMenu/browser_contextmenu_input.js
rename : browser/base/content/test/general/contextmenu_common.js => browser/base/content/test/contextMenu/contextmenu_common.js
rename : browser/base/content/test/general/ctxmenu-image.png => browser/base/content/test/contextMenu/ctxmenu-image.png
rename : browser/base/content/test/general/subtst_contextmenu.html => browser/base/content/test/contextMenu/subtst_contextmenu.html
rename : browser/base/content/test/general/subtst_contextmenu_input.html => browser/base/content/test/contextMenu/subtst_contextmenu_input.html
rename : browser/base/content/test/general/subtst_contextmenu_xul.xul => browser/base/content/test/contextMenu/subtst_contextmenu_xul.xul
extra : moz-landing-system : lando