tools: wordlist-xml2json: fix for large files

Need to read line-by-line or encode seems to get confused with files >
2048 bytes.

Also trim words.
Ported wordsgame activity

... by extending and deriving from gletters. Some changes:

  - fixed memory leak of finished words
  - highlight typed letters
  - drop-rate and speed are calculated differently for wordsgame
  - drop-rate and speed are now also increased for gletters
    between sublevels
  - keys on VirtualKeyboard are now sorted
click_on_letter: update to new Score anchors
 Merge branch 'integration-master' into 'master'

Wordsgame

Hi,

this ports wordsgame by extending and deriving from gletters. For changes cf. notes in commit msg.

Thanks, regards,
  Holger