Bug 1022575 - Received SMS store (without text) on check balance. v2.0 only patch. r=julien

As discussed on IRC, I'll leave it as it is now to be closer to real thread list markup. I've tried to use "ThreadListUI.appendThread" inside ```insertMockMarkup```, but it broke several tests that spy on ```appendThread``` and expect exact number of its calls. Will make it in the next related non-blocker patch though.