fix how options work for movedata_cols given as indices

[CarlijnB]

Privacy functions don't work if movedata_cols are given as col indices.

Probably need to ensure replacement of col indices with col names in movenetenv$options, as original col indices are meaningless in any downstream data processing/analysis

[CarlijnB]

Replacement of col indices with col names, currently works like so:

• at reformating data stage, if movenetenv$options$movedata_cols has any integers, colindex2name() [read_movement_data.R] is called
• colindex2name() returns a list of lists (list(minvars,extra)) , containing the options with values in the form of col names
• this list is then used internally within reformat_move_data(), but the translation from col indices to col names is not saved anywhere outside the function.

Suggestion is to save this translation directly within movenetenv$options$movedata_cols.

Are there any downsides to doing so?

• What if combining datafiles, where data are consistently in the same col order, but with varying col names? Then it'd be handy to maintain col indices for reading multiple datafiles

[CarlijnB]

Could create a second "options list", movenetenv$translated_options ?
but this might require adapting the config system, to allow users to change either set of options