[FEATURE] tmt 10plex support

This pull request adds tmt10plex support to OpenMS. Additionally, it extends `IsobaricChannelInformation`

 * switched from int to String for channel name (required for support of tmt 10plex)
 * added specific isotope impurity definition -> each channel has to declare to which channels his -2,-1,+1,+2 isotopes will contribute

 
`itraq4plex` ? cpoy paste error? I am confused?