* if an encoding is explicitly specified, use it and don't guess
* otherwise guess and return the guessed encoding so it can be
displayed in the configuration UI
* fix less-than-stellar configuration & behaviour of select2 inputs
to properly reflect underlying values as they get modified, to
correctly handle future configuration guesses
* Handle a leading + in import data, some contexts (e.g. bank
statements) will mark positive sums explicitly for clarity
* Add basic grouping/decimal separator inference for people importing
data from many localisations or to avoid them *having* to configure
their separators if we can handle it for them, currently very basic
Xavier Morel