Fix British English spellings
dialogue      -> dialog    (when referring to GUI window items)
analogue      -> analog
color[s]      -> colour[s]
colorspace    -> colourspace
visualization -> visualisation
normalize     -> normalise
Harddisk      -> Hard disk (consistent with all other usage of "[Hh]ard disk")
disc          -> disk      (context: magnetic media)
disk          -> disc      (context: optical media)

'colourspace' -> 'colour space' nitpick
Merge pull request #3261 from MilhouseVH/english-fix

Fix British English spellings