Removed external folder
Adds external submodule
Updates travis-script, removed using download-deps.py now, 'external' is
a submodule module now. please use `git submodule update --init` to
fetch it.
Re-adds resources in cpp-tests and lua-tests, but removes some large
files. We need to reuse some resources when doing some tests.
Xcode project fix
Removes download-deps.py, using `git submodule update --init` to get the
external libraries. Thanks.
Merge pull request #6571 from dumganhar/re-add-res

'external' folder is a submodule now, re-added resources for cpp-tests and lua-tests except large files