This commit also adds a tool to push translation sources to Transifex.
This tool makes sure that we don't push mobile source file. Mobile
source file is supposed to be handled from Zulip-Mobile repo.
This reverts commit ba8dc62132.
As best I can tell, the old configuration was correct for what Django
wanted. Further testing is required, but this at least brings
.tx/config to match the actual filenames; I think our Chinese
translations have been broken until now.