Add "rewriteable" to UK dictionary

[DimitriPapadopoulos]

While "writeable" is part of the en_GB-large dictionary "rewriteable" is not.

Both "writable" and "rewritable" are part of dictionaries.

• Cambridge
• Collins

From the Google Books Ngram database:

• https://books.google.com/ngrams/graph?content=rewriteable%2Crewritable&year_start=1800&year_end=2019&corpus=en-2019
• http://app.aspell.net/lookup-freq?words=writeable%0D%0Arewriteable%0D%0Awritable%0D%0Arewritable;also=similar;parm=full