More even way of zooming

Fixes the extra comment in #570. This is something that I have also found strange. Adobe Acrobat X and other PDF viewers also zoom with steps of at least 10%. With this setting, one can always reach 100% and zooming in and out is more even (100 - 110 - 120 % etc. instead of 100 - 106 - 113 etc.). In the higher ranges, the zooming percentages will grow faster, just like in Adobe Acrobat X for example.