Modifiers implementation, random words, random query types, difficulty, etc.

[LoanR]

Four random modifiers:
espagnol | random word | lexical field | rhyme | phonetic | french | ...

Four difficulties:

• economic - keep unspent time between words (no time bonus score)
• exponential - more and more unfrequent, long, special chars... (automatically better score, maybe more multiplier)
• slower - start with a smaller words per minute ratio (smaller multiplier)
• no break - no preparation time between levels (better level score multiplier)

=> modifiers are no longer 'exclusive' but can share a same value -> modifiers with same value are unchecked.