Creating files & writing metadata for fixed experiments
Adding code to handle fixed spectra

- Added starting pulse length/number of steps to metadata
- Changed fileHandler to take an extra argument (starting pulse length)
- Changed fileHandler to store pulse length in 'frequency' variable for fixed spectra only
- Changed exporting spectrum data to print correct column title (freq/pulse length) depending on spectrum type
- Changed stepSize for fixed spectra, to store step size in ticks (step in pulse length)
Changed metadata format in (hopefully) all necessary places

To accommodate extra 2 pieces of data