STA2 header line of GSE2 files

The GSE2 manual defines a (mandatory! see [pdf](https://github.com/obspy/obspy/blob/master/obspy/gse2/docs/provisional_GSE2.1.pdf) page 66, table 6) second header line that we currently do not parse (and also *do not write*!). Besides the *network code* (albeit possibly SEED-non-conform 9 chars long), it can contain other useful information, namely *station coordinates*:
```
Position  Name       Format                 Description
   1-4   "STA2"   a4        Must be "STA2"
  6-14   Network  a9        Network identifier
 16-34   Lat      f9.5      Latitude (degrees, S is negative)
 36-45   Lon      f10.5     Longitude (degrees, W is negative)
 47-58   Coordsys a12       Reference coordinate system (e.g., WGS-84)
 60-64   Elev     f5.3      Elevation (km)
 66-70   Edepth   f5.3      Emplacement depth (km)
```
In principle we should definitively parse that information.. the problem is that I have seen data from two different sources and both do not adhere to the exact positioning as given in the manual, see e.g. [one of our test files](https://github.com/obspy/obspy/blob/master/obspy/gse2/tests/data/loc_RNON20040609200559.z):
```
STA2           -999.0000 -999.00000              -.999 -.999
```
For example the longitude field goes from 26-35.
A header from another file I saw looks like this (numbers changed):
```
STA2 ABCD       12.34567    1.23456 WGS-84       -123.456 1.234
```

So, to sum it up, currently we are potentially missing useful header information when reading from GSE2. But on the other hand, the data out there seems to not adhere to the official manual. So I am not sure what to do about it.