Bundle up icu, libical and opendkim libraries for Cyrus.

Based on part of Bron's email to the cyrus-devel list:
https://lists.andrew.cmu.edu/pipermail/cyrus-devel/2015-September/003483.html

This project uses submodules, so clone it with the --recursive argument.

Usage:

    make all        # do all the compilations
    make install    # install them to $PREFIX (uses sudo)
    make clean      # clean up the build directories (doesn't remove sources)
    make update     # grab newer versions of the sources

(You can also make foo, update-foo, clean-foo and so on to target them one at
a time.)

icu sources are from release-55-1 from the icu subversion repository (change
$ICU_RELEASE in the Makefile to have `make update` pull a different version).

libical and opendkim are built from git submodules (master branch in each
case).

See Makefile for the nitty gritty.

When compiling Cyrus, you'll need PKG_CONFIG_PATH set to contain the installed
pkgconfig directories (there may be multiple, e.g. architecture/platform
specific ones).

Try something like this to get a complete list:

    find /usr/local/cyruslibs-fastmail-v1 -type d -name pkgconfig | paste -sd: -

You also need to let ld know about the new lib directories.  You can set
LDFLAGS as Bron suggests, or add them to your ld config, something like:

    $cat /etc/ld.so.conf.d/cyruslibs-fastmail-v1.conf
    /usr/local/cyruslibs-fastmail-v1/lib
    /usr/local/cyruslibs-fastmail-v1/lib/x86_64-linux-gnu