Revert "Remove unused mako option"

This reverts commit 3c28ff454fc2209c2df18e94e5650da35ff86c10.

The `escape` isn't declared explicitly, as it was already a [default
filter](http://docs.makotemplates.org/en/latest/filtering.html#the-default-filters-argument),
used in *all* expression tags (except in those using `|n`).

MarkupSafe is pulled in as a dependency of Mako, which Adhocracy depends on, so
this hasn't only worked *by accident*.

Using `escape` from *MarkupSafe* is recommended in the [Pylons 1.0.1 upgrade
notes](http://docs.pylonsproject.org/projects/pylons-webframework/en/latest/upgrading.html),
that's why I changed it in the corresponding commit
db63816f1f012d231a838077a314d55e6ba54114.