gnu-maintenance: Move FTP directory info to 'properties' fields.

gnu-maintenance: Move FTP directory info to 'properties' fields.

* guix/gnu-maintenance.scm (ftp-server/directory): Rewrite to honor
PACKAGE's properties.  Remove list of quirks.
(releases): Add #:server and #:directory parameters.  Remove call
to 'ftp-server/directory'.
(latest-release): Likewise.
(latest-release*): Add call to 'ftp-server/directory'.  Honor
'upstream-name' property of PACKAGE.
* gnu/packages/fonts.scm (font-gnu-freefont-ttf): Add 'properties'
field.
* gnu/packages/gnupg.scm (libgpg-error, libgcrypt, libassuan):
(libksba, gnupg): Likewise.
* gnu/packages/gnuzilla.scm (icecat): Likewise.
* gnu/packages/package-management.scm (guix-0.10.0): Likewise.
* gnu/packages/pretty-print.scm (source-highlight): Likewise.
* gnu/packages/scheme.scm (mit-scheme): Likewise.
* gnu/packages/telephony.scm (ucommon): Likewise.
* gnu/packages/tls.scm (gnutls): Likewise.