[WIP] change FixerInterface

Resolves #867

proof of concept

Some very old work (from september!), need to rebase on master.
It still need much work to be done, but maybe it will be usefull for somebody

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TODO: 
- [X] implement changes
- [ ] reactivate AlignDoubleArrowFixer after #905 is solved
- [X] fix detection of change: SingleLineAfterImportsFixer (PSR2)
- [ ] fix detection of change: FunctionDeclarationFixer (PSR2)
- [ ] fix detection of change: BracesFixer (PSR2)
- [ ] fix detection of change: AlignDoubleArrowFixer (CONTRIB)
- [ ] fix detection of change: AlignEqualsFixer (CONTRIB)
- [ ] fix detection of change: OrderedUseFixer (CONTRIB)
- [ ] make the tests pass
- [ ] check performance difference
done