Improve the way the Remaining Estime is showed on current fields (XLSX)

As a user, I should see the output of the field "Remaining Estimate" as the same way that's shown on JIRA.
For now, the Xporter print the correspondent value of the Remaining Estimate in seconds/day.
For example: when we have "1d" on remaining estimate field, the Xporter prints "28800" instead of prints the same result as JIRA.