build: i18n: add icu config options

Make "--with-intl=none" the default and add "intl-none" option to
vcbuild.bat.

If icu data is missing print a warning unless either --download=all or
--download=icu is set. If set then automatically download, verify (MD5)
and unpack the ICU data if not already available.

There's a "list" of URLs being used, but right now only the first is
picked up. The logic works something like this:

* If there is no directory deps/icu,
  * If no zip file (currently icu4c-54_1-src.zip),
    * Download zip file (icu-project.org -> sf.net)
  * Verify the MD5 sum of the zipfile
    * If bad, print error and exit
  * Unpack the zipfile into deps/icu
* If deps/icu now exists, use it, else fail with help text

Add the configuration option "--with-icu-source=..."

Usage:
  * --with-icu-source=/path/to/my/other/icu
  * --with-icu-source=/path/to/icu54.zip
  * --with-icu-source=/path/to/icu54.tgz
  * --with-icu-source=http://example.com/icu54.tar.bz2

Add the configuration option "--with-ic...