Fix the people picker freezing issue

[gautamdsheth]

Q	A
Bug fix?	Y
New feature?	N
New sample?	N
Related issues?	fixes #128 , #134

What's in this Pull Request?

As mentioned in #128, people picker component freezes when you try to add another user. This happens in the local as well as SharePoint workbench because primaryText is undefined. So, modified it to use secondaryText. This fixes the freezing issue and we are able to add multiple users

[estruyf]

Thanks @gautamdsheth appreciate the fix, but implemented another fix myself. The issue why primaryText is undefined comes from the fact that in the latest versions of Office UI Fabric the properties changed. Before the NormalPeoplePicker used primaryText where it now uses text. All references of primaryText had to be updated in the code instead of falling back on secondaryText. Although this was a good approach, it does not cover all. Will close this PR without merging it, but you will receive credits in the changelog for this.

Thanks.

[gautamdsheth]

Thanks @estruyf for such a detailed response. I should have investigated it more and should been more careful before sending this PR, apologies.