fix #311: replace confusing error dialog by a toast

* replace confusing error dialog by a toast
* fix an i18n issue with "error_refresh" messages
* unification of refresh messages (Toast everywhere: notificaitons, comments, pages, posts, media, themes) not sure about stats: #567
Merge branch 'develop' into issue/311-confusing-error-dialogs

Conflicts:
	res/values/strings.xml
Merge pull request #568 from wordpress-mobile/issue/311-confusing-error-dialogs

fix #311: replace confusing error dialog by a toast