Improve the flexibility of the extract.metadata.svc function

[serbinsh]

SVC likes to revise their file headers and the lazy parsing of the header info to include the spectral-level metadata breaks when a new row is added in the header because it assumes fixed line numbering. Instead we need to read the header, find the lines of interest (e.g. gps time, lat, long) and then provide the line number associated to read out the info.

This issue arose using a newer HR-1024i which has a slightly different header than an older serial number.

Issue caused by lazy coding