0.8.1

This release fixes some bugs, mostly GUI-related:
- corrected handling of invalid start, stop, step parameters combination when calculating spectra;
- fixed incorrect floats' rounding in numeric entries;
- added reaction (trim conformers/redraw spectra) to "Enter" keypress, when editing a numeric entry;
- fixed an error occurring when "show activities" is checked but there are no activities in a plotting range;
- added auto-update of energies-related values after trimming.