Use Excel types instead of Strings

The column Created, Updated, Time Estimate and Time Remaining cannot be used for further processing inside Excel. The reason is that the data is a String instead of a date / numeric value.

For example it would be nice to know the estimated remaining time per developer and project, and Excel could be used to implement the grouping and summing up the individual values. Problem: Excel (at least the german version) does know know how to sum "2 days" and "5 days" because those are Strings, not numbers.

For the Created and Updated columns it might be sufficient to do the i18n correctly. Right now I get a mix of german words and english notation: "8/Mai/03". If I change that to the correct german notation "8. Mai 03" Excel recognizes the String as a date and I can sort the line accordingly.

Not sure if Jira would benefit from other server/client language combinations (see environment description).