Inner join handle common columns

[Vindaar]

- *Potentially BREAKING behavior*: ~innerJoin~ now has another
  parameter ~commonColumns~, which handles how columns that are common
  to both dataframes are handled.
  Previously, we wrongly assumed that the data in all common columns
  must match exactly. In that case it didn't matter which column to
  take.
  However, if they did *not* match, the data for the common columns
  (including the one we joined by) was corrupted and left at default
  initialization from the first mismatch in a common column.
  There are now 3 different ways:
  - ~ccLeft~: keep the data of the left input
  - ~ccRename~: Rename the common columns to ~*_left~ and ~*_right~
    (default)
  - ~ccDrop~: Drop common columns that are not the joined one.
  We choose to use ~ccRename~ as the default, because it keeps all
  information. It is a breaking change however, because the common
  columns now have a different name. But imo it's better here to make
  people aware that this change happened instead of giving them wrong
  data.
  Feel free to conflict me on this.

[Vindaar]

Merging despite CI failures. Those are unrelated (due to nimcuda) and will be fixed separately.