Channel/Systemmatic enums

[dteague]

I started doing this with my open PR (#32 ), but it might be good to expand this to also the chans and systematics. My gripe being that I wish these things were virtual but with enums, you really can't do that. Putting more generic variables and functions in the selectorBase makes sense, but with these ever expanding lists and maps, I think it would be good to switch over to something different for this

I've made the "dynEnum" class to get around this (it's not very sophisticated) to handle this problem. I'm sure there are better solution, so we might want to think about this. Especially since there is the nifty histLabel class you've made to handle adding histograms. I might link to some code snippets if I think of anything.