Fix splitting in FromQEOutput.read_frequency_file

[singularitti]

Sometimes we have imaginary frequencies for our materials. And QE prints them out in negative numbers. If the number is too long, it may coalesce with the previous one, like below:

           -0.222230 -0.355470  0.344040
-1447.3713-1187.8571  -80.3199  329.8292  833.3836 1105.8035

So this will cause read_frequency_file not be able to read the frequencies correctly. In this change I want to make it split either at a minus sign or at a space.