Reported in forums

1. Add custom variables report
2. Switch to graph
3. Add 'conversions' to graph (button on top of graph)
4. Switch to table
5. nb_conversions column present on table

Solution: we should translate all column names even those unused.

Also I think we could really simplify the whole code of AddColumnsMetrics* since it's confusing and not very modular nor loosely coupled.

The viewDataTable=tableGoals should only be a proxy to the set of columns to display. The views would also work when columns are manually specified via &columns= and would be then processed from the raw columns, in one main AddProcessedColumnsFilter with a list of a columns as input, which will call other smaller filters to add new and processed and goal metrics.

This simplification / refactoring of code around management of columns and metrics would for sure be helpful in many ways in the future, such as building Custom Reports and adding Custom Metrics via hooks that would add the Metadata metrics information, but could also easily hook the new metrics SQL inside the core archiving query.

This would also be useful for later defining new Custom Dimensions based on Custom Variables, but with their own reports and set of metrics.