Correct dysfunctions & compability interpolate / no interpolate logics

- 'next' & 'prev' buttons do not work with slices higher than file time
step
- Correct wrong results when interpolation factors (slices per update /
per hours) are not miltiple or submultiple of hours
- Ensure accuracy when interpolation situation(FS#1087)
- Correct dysfuntion with Linux (combobox doesn't reacts the same way as
with Windows)