setup.py: add babel to dependencies

Status Job ID Name Coverage
  Build
created #18817
build:2.7
created #18818
build:3
 
  Test
created #18820
allowed to fail
lint:2.7
created #18824
allowed to fail
lint:3
created #18819
pyflakes:2.7
created #18823
pyflakes:3
created #18821
unittests:2.7
created #18825
unittests:3
created #18822
allowed to fail
unittests-modules:2.7
created #18826
allowed to fail
unittests-modules:3
 
  Deploy
created #18827
doc:2.7
created #18828
doc:3