Fix British English spellings

This is an update of PR #3239 (see comments on Martijn's merge 211c36f8af5f11efded952bf9368e15da766f39d of 3239).

```
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)
```