added various longslit related tasks
added mhvk's copper argon line list
added some of MHVK's documentation
added the longslit arcs setup.
fixed wrong keyword
linking longslit arcs procedure finished
in the process of implementing longslit calibration
updated representation for longslit
in the process of saving the wavelength calibration to the database
finished the wavecal. updated the documentation
Merge pull request #43 from wkerzendorf/gmos/longslit_wavecal

[WIP] longslit wavecal
removed the link of the science set to the longslit arcs. this step should happen when wavelength calibrating the slitlets.
Merge pull request #44 from wkerzendorf/gmos/update_science_sets

Removing the Longslit calibration from the sciencesets
Only fit central range for long-slit arc