Add educational mode

[queleok]

In this mode the following changes to the looks of the verified words would apply:

• words become links to their definitions in google dictionaries (probably it makes sense to do this by default) Decorate verified words as links #10
• phonetics are printed after each word Ed mode: add phonetics for verified words #11
• button to listen to the transcription of the word becomes available Ed mode: add transcription playback for verified words #12

Beside that it would probably make sense to change the rules of the game a little bit:

• all available letters can be used arbitrary number of times Ed mode: allow re-using given letters arbitrary number of times #13

Each of these points deserves its own case, so let's consider this as an umbrella case for discussions with actual implementations done elsewhere.