Refactor some code, with a perspective of a complete editor

We'd like to Refactor A4, think its code as we can let it grow and add lots of feature without became mad :P
Assegnee should think how to split feature and make a cool module structure, should think about how to handle representation of the image different from the 'practical' SVG (so we can handle other format in future, and to make an abstraction level around svg and its complexity)