QE's force constant file format has changed, breaking QEParser::parsePhHarmonic

[BogdanRajkov]

QE has recently changed the format of the force constant file (.fc) in a backwards-incompatible way. In addition to the dielectric constant and the Born effective charge tensors, the .fc file now also contains the constant alpha, which is related to the long-range dipole-dipole correction to the interatomic force constants. For a further discussion, see the relevant issue.

Importantly for us, the .fc file previously contained a line that was either "T" or "F", depending on whether the .fc file contains the dielectric and Born charge tensors. Now, if the .fc file contains these tensors, the same line will be "T", followed by the value of alpha. Phoebe's parser needs to updated; here you can find the relevant change to QE's own parser of the .fc file.

To maintain uniformity across different parsers, we should treat alpha the same way we treat bornCharges and dielectricMatrix, i.e. by including it in the Crystal class. For QEParser, if no value is provided in the file, then we have to use the backwards-compatible default value that previous versions of QE were using.