Use obs_channelid when listed for event screenshot and movie generation

[Keith Hughitt]

HEK Events may include information about the channels a particular event has been observed in. This information is stored in a parameter "obs_channelid".

Example:

http://www.lmsal.com/hek/her?cmd=export-voevent&cosec=1&ivorn=ivo%3A%2F%2Fhelio-informatics.org%2FAR_SPoCA_20101007_102424_20100905T014900_6&rev=1

In many cases, the identifiers used for the channels correspond with the "name" parameter in the Helioviewer datasources table. In other cases, however, either the identifiers differ or Helioviewer may not recognize the channel specified, e.g.:

"EUV", "visible", "XRA", "211"

(ex. http://www.lmsal.com/hek/her?cmd=export-voevent&cosec=1&ivorn=ivo%3A%2F%2Fhelio-informatics.org%2FSS211_TomBerger_20100629_212319)

To get around this, Helioviewer can attempt to "guess" at what the intended channels are, and fallback to some default choices if it cannot guess any sources:

foreach obs_channelid.split(","):
   if (like "171"):
      // Assume AIA 171

etc.