no more unflagged column

• i removed the unflagged column at all.
• now History() takes a mandatory index at creation an nothing more.
• to create a History from data (hist-df, mask-df, and meta list) one can call createHistory(..)
• History.max() still return UNFLAGGED, even for empty Histories, which is possible now because of the inital passed index

only this commit - !285 (73708889) is relevant, the rest comes from historymeta (!284 (merged) )

i dont know where the translator rely on the UNFLAGGED-column, but this we need to adjust, i guess..

i also dont know if we want to go down the line, but i would say we have to decide which way we want to go:

• a) without UNFLAGGED-column with quite simple history-creation, (mandatory index to __init__)
• b) with UNFLAGGED-column, more complex History creation (hist, mask, meta are needed), except passing no args at all (empty History)