[enh] #807 transfer amount can be given in current referential

src/sakia/gui/sub/transfer/controller.py

src/sakia/gui/sub/transfer/model.py

src/sakia/gui/sub/transfer/transfer.ui

src/sakia/gui/sub/transfer/view.py

src/sakia/money/base_referential.py

src/sakia/money/percent_of_average.py

src/sakia/money/quant_zerosum.py

src/sakia/money/quantitative.py

src/sakia/money/relative.py

src/sakia/money/relative_zerosum.py