hexchat-build.ps1: Build script to build all deps and Hexchat.

Automates build steps at http://gtk.hexchat.org/ and http://docs.hexchat.org/en/latest/building.html
Some assembly required. Read the script for instructions.
Re-saved pango-language-sample-table.h with BOM because cl.exe throws C2001 otherwise.
gtk: Patch to fix crash on right-clicking tray icon.