Add XRegExp from https://github.com/slevithan/xregexp/tree/d06eff50f87d81d2dd3afc1e854784c38b17bcc4/src
Load XRegExp into Zotero.XRegExp and Zotero.Utilities.XRegExp and make it accessible from translators.
Remove unnecessary character classes. Add some useful ones.
Merge remote-tracking branch 'aurimasv/xregexp' into 3.0
Tweak loading process
Fix source files to be UTF-8