Allow user to chose the time tracking base unit to simplify interface with JIRA Merged

Currently, for the time tracking interface to work between Aha! and JIRA, the JIRA time tracking base unit must be in minutes.

Otherwise the values passed through the interface will be grossly inflated:

https://support.aha.io/hc/en-us/articles/206032335-Jira-time-based-estimates-inflated-from-Aha-estimates

There are many situation where changing the base unit in JIRA is difficult and cannot be achieved easily (for example when a lot of projects are already setup with many different external tools and reporting)

A solution would be to offer the possibility to configure the default time unit in Aha! interface as well. This could simply be done in the definition of the interface without impact on the actual value being stored in Aha!