Fix TestLanguagePack tests by mocking only when necessary

(test failures following safe_signals removal)
Make update_incompatible_versions() reload the addon before trying to use it

Fixes addons.tests.test_models:TestAddonModels.test_no_change_deleted following
safe_signals removal.
use .gitkeep instead of .gitignore; bug 687408
Try fixing mkt.stats.tests.test_views failures by mocking search indexing
Fix for editors.tests.test_views.TestPendingQueue.test_get_queue
missed a possible None in es_app_to_dict
Commit from Mozilla Verbatim by user jasnapaka@jasnapaka.com.: 4945 of 5474 strings translated (5 fuzzy).
add italian (bug 918560)
document ?region in search API (bug 917500)
fix field names in search.rst