Sorting and filtering improved

- Alphabetic sorting of Category, Footprint, Temp and Supplier.
- Sorting now understands fS, ppm, p, n, µ, m, K, M and G
  prefixes in the columns Value, Current, Power and Tolerance.
- Spinbox for price now have 6 decimals.
- Update of category and footprint comboboxes fixed in main view.