fixed label overflow issue

[akmorrow13]

There has been an issue with long label names, shown here:

The fix shows ellipsis for long labels but allows you to hover to get the full name.
Without hover (Variants label):

With hover (Variants label):

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This change is 

[coveralls]

Coverage increased (+0.04%) to 91.01% when pulling c4eac19 on akmorrow13:labelFix into 499de4e on hammerlab:master.

[armish]

thank you, @akmorrow13 -- really nice addition.