Output NODES and PROCS variables in export headers

[PierreS-alpha]

Related to PR #180

Initial demand: Colleagues from Formaterre asked us to output some GNSS metadata in export header.

Request verbatim

j'ai testé le fichier webobs, en fait il me manque 2 choses importantes pour les intégrer:
    - le nom de la station dans l'entête: # STATION_NAME : PMZI00MYT
    - le nom de la solution à intégrer dans la base de données.
    D'autres informations sont manquantes:
    - la constellation, par défaut je mets G: # CONSTELLATION: G
    - la refFrame, par défaut je ne mets rien: # REF_FRAME: IGS20

Ideas after discussions with @beaudu:

• more polyvalent export for any superproc, with 2 new keys in the PROC config:
  • EXPORT_HEADER_PROC_KEYLIST
  • EXPORT_HEADER_NODE_KEYLIST
• Separate with a dot:

# NODE.A_FIRST_KEY: value
# PROC.ANOTHER_KEY: blabla

[beaudu]

The WebObs steering committee validated the polyvalent export procedure, but recommend in this case:

• to export only NODE.CHAR9 key so users can link to M3G/Glass metadata services to get any other updated information (station name and location, constellation, etc).
• the reference frame name will be specific to the proc configuration (e.g., local referential)

[PierreS-alpha]

The preliminary export design had the following structure:

# NODE_FID: DSD0
# NODE_NAME: "La Desirade (Guadeloupe)"
# NODE_GNSS_9CHAR: 
# NODE_LATITUDE: 16.308030
# NODE_LONGITUDE: -61.060191
# NODE_ELEVATION: 272.00
# PROC_ITRF_REF:  ITRF20(CF)
# PROC_VELOCITY_REF:  0,0,0
# PROC_VECTORS_VELOCITY_REF:  12,15,0

Following yesterday's discussion and present comment, it should look:

# NODE.FID: DSD0
# NODE.NAME: "La Desirade (Guadeloupe)"
# NODE.GNSS_9CHAR: DSD00GLP
# NODE.LAT_WGS84: 16.308030
# NODE.LON_WGS84: -61.060191
# NODE.ALTITUDE: 272.00
# PROC.ITRF_REF:  ITRF20(CF)
# PROC.VELOCITY_REF:  0,0,0
# PROC.VECTORS_VELOCITY_REF:  12,15,0