Configure www.mcga.gov.uk with global path preservation to dft.gov.uk

This config change is to accommodate the combination of www.mcga.gov.uk into the DfT main site at www.dft.gov.uk/mca

There are some additional rules in bouncer required to make this particular transition work fully in the transition app.

I think this comment would be clearer written like this:
```
# This global_redirect_append_path peforms redirects at the site root:
#
#   www.mcga.gov.uk/foo/bar       --> www.dft.gov.uk/mca/foo/bar
#
# Additionally, we have rules in Bouncer which are applied before the global
# redirectwhich perform redirects like this:
#
#   www.mcga.gov.uk/c4mca/foo/bar --> www.dft.gov.uk/mca/foo/bar
#   www.mcga.gov.uk/mca/foo/bar   --> www.dft.gov.uk/mca/foo/bar
```

I've also made minor corrections - for example it should be www.dft.gov.uk rather than dft.gov.uk.