Show 'labelName' in version history dialog when present

when a document gets branched, for example for 'Christmas 2017' campaign, it is nice if we can see this label in version history dialog. Note that this label is different than the jcr version history label. The label we show in the version history dialog is a label name which is allowed for example on publishable hippo documents. Note that on variant nodes we will also include the label as is in version history, but this is a more cryptic label. For example on the live variant we might have:

- hippo:jcrlabel = v8UfB-live

(v8UfB is for example id of Christmas 2018 branch).
On the preview variant we might have

- hippo:jcrlabel = v8UfB-preview
- hippo:labelname = Chirstmas 2018

In version history, there can be frozen nodes for this preview variant that have

- hippo:jcrlabel = v8UfB-preview
- hippo:labelname = Chirstmas 2017

Where the labelname is 2017 instead of 2018! This is because the labelname is detached from the real branch (in this example the branch got for example a year later renamed to 2018 but still with id v8UfB)