Update en_GB English (United Kingdom) with 823 strings, 100%.

Checked and translated the 823 untranslated strings, applied fixes and corrections.
File now has 100% translated strings.
Summary:
color > colour
localize > localise
localization > localisation
optimize > optimise
organize > organise
organizations > organisations
pluralize > pluralise
summarizing > summarising
synchronized > synchronised