Use ICU instead libutf8proc for Unicode-9 character width

[yan12125]

ICU is already a dependency of qt5-base, at least on Arch Linux. Using ICU can reduce headaches of packagers. For example, on Arch Linux, there's already a utf8proc package at https://www.archlinux.org/packages/community/x86_64/libutf8proc/, but it's an old 1.x fork by netsurf. Also, I guess ICU is better maintained than utf8proc.

This needs to be upstreamed to Konsole as it's still using ancient Unicode 5.0

Update 2017/09/27: Android uses ICU to implement wcwidth(): https://android.googlesource.com/platform/bionic/+/c41b560f5f624cbf40febd0a3ec0b2a3f74b8e42

[apjanke]

ICU is not a dependency of Qt on Mac Homebrew, but it's an easily installable separate package (icu4c), so I wouldn't think it would be a problem to add the dependency there, too.

[yan12125]

The utf8proc patch was created to workaround mismatch between Unicode 8 in glibc and Unicode 9 in some other programs. Given that glibc has upgraded to Unicode 9 in version 2.28, and I haven't heard another issue in Unicode 10 or 11, I think the utf8proc patch can be removed.

Also, due to the ABI policy of ICU, using it means that users need to rebuild QTermWidget often. It's a burden.