build: New API key for Google

Some bugs in evolution-data-server were causing us to hit Google's
daily limit for the CalDAV and Tasks APIs. The bugs have since been
fixed, but until every single user out there installs the fix,
everybody using the old keys will be susceptible even if they have a
fixed copy of evolution-data-server. This is because Google identifies
us by the API key and not the version of the code running on the
client.

We are therefore phasing out the old key, so that users updating their
systems have no connection to the one that was tainted by these bugs.

https://bugzilla.gnome.org/show_bug.cgi?id=771547
https://bugzilla.gnome.org/show_bug.cgi?id=773248