Added fix for lack of curve coloring when loading data into the gui.

Hi Nathan,

here's a quick survey of the issue itself and what I did to fix it.

**THE ISSUE:**
When loading whisker or measurement files already tracked manually, the data is loaded correctly but no identity is set. Hence whiskers have a red color and are highlighted only when selecting whisker ID -1. The user is unable to continue tracking / correct errors on videos with more than one whisker.

**THE FIX:**
I used the `setIdenity()` function to initially set the idenity for loaded whiskers and measurements; see `updateIdentity_()` .

Take care, best regards,
Viktor