Add dnscrypt channel in unbound by default

[rootwyrm]

From the manual:

The  dnscrypt: clause gives the settings of the dnscrypt channel. While
       those options are available, they are only meaningful  if  unbound  was
       compiled with --enable-dnscrypt.  Currently certificate and secret/pub-
       lic keys cannot be generated by unbound.  You can use  dnscrypt-wrapper
       to  generate those: https://github.com/cofyc/dnscrypt-wrapper/blob/mas-
       ter/README.md#usage

[rootwyrm]

Moving this to 2.0.x, because it's just going to be entirely too much work without finalizing the PKI first.