Copy env's pybabel into base dir to fix string extraction

The jinja2 extracter needs to know about our custom HighlightExtension (used on
pages such as get-involved/develop/applications), which is not in the env's
python path. Copying pybabel into the base dir gives it access to our modules.
This is only required for string extraction; other scripts use pybabel from the
env directly.

If the env's pybabel version is updated, this copy must also be updated.

extract-messages.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 . ./translation.vars
 
-TZ=UTC env/bin/pybabel extract --msgid-bugs-address="http://trac.i2p2.de" \
+TZ=UTC ./pybabel extract --msgid-bugs-address="http://trac.i2p2.de" \
                                --project=$PROJECT \
                                --version=$VERSION \
                                -F $BABELCFG \