Mirror Evolution calendar settings into our own schema

Mirror Evolution calendar settings into our own schema

Right now, we are hard-depending on the presence of Evolution by
using its settings schemas. This is likely to be unpopular, and
also causes instability if someone happens not to have Evolution
installed, so install a schema that has the same data path as
the Evolution schema, but a different name and install that
for the keys we need.

To avoid a string-freeze break, we rely on the translations in
Evolution - if Evolution isn't installed, the key descriptions
will be untranslated in dconf-editor.

https://bugzilla.gnome.org/show_bug.cgi?id=674424