Harmonize SeparationColumnType and RetentionIndexType

[eselmeister]

Over the years, two strategies how to handle column specific retention index values have been added and used. Hence, both

• RetentionIndexType
• SeparationColumnType

shall be harmonized to enable modifying the column mapping at a central place instead of several:

org.eclipse.chemclipse.model.core.RetentionIndexType
org.eclipse.chemclipse.model.columns.SeparationColumnType

RetentionIndexType mappings in *.msl, *.msp and *.cal files.

Parse Separation Column from Header
org.eclipse.chemclipse.msd.converter.ui.ConverterPreferencePage
org.eclipse.chemclipse.swt.ui.preferences.PreferencePageSystem

[eselmeister]

As this task will be complex and requires the modification of several positions in the source code to ensure backward compatibility, I'll personally take care of it.