When the date custom fields are empty, an invalid format date is displayed, and prefix should be put in the custom fields of the Test Execution in order to distinguish them

Short Description: When the date custom fields are empty in the issue details, an invalid format date is displayed. And when adding the custom fields of the Test and TE, some of them are displayed with the same name, thus not being possible to distinguish them. We should add a prefix to the test execution fields in order to distinguish them from the test fields.

Steps to Reproduce:

1 - Add the Test Runs List gadget to the Dashboard
2 - Add the following columns: "Version", "End Date", "XRay End Date", "Start Date", "Begin Date", "XRay Date", "Revision" and "XRay Revision"

*Actual Result: *Verify that there are two columns named "End Date", one displaying the information of the test issue and the other displaying the information of the test execution issue. Start Date column should be also called Begin Date when added to the configurable columns.

Expected Result: We should put a prefix to distinguish the test execution fields

5 - Now, create a new test execution for the test issue, but leave the date fields empty and refresh the gadget

Actual Result: A non valid date format is displayed

Expected Result: The columns should be empty