morse_code, activity

Rework from https://github.com/gcompris/GCompris-qt/pull/179. (I will have to do a first commit with the original code, and then one with updates)

The code reuse the layout of roman numerals and the map from braille alphabets.

It works 3 levels per 3 levels:

• First find the morse values for the characters
• Find the characters with the displayed morse value
• Audio mode to play the morse value and find the corresponding character.

There are 3 datasets:

• 1 dataset for letters
• 1 for digits
• 1 with words (non translatable English words to be sure we only have ascii letters)