Label changes

[hrojek]

Change application names:
"Retrieval" to primeqa.retrieve", "Reader -> primeqa.read", and "QA" to "primeqa.answer".

Change the titles color to dark blue and its size from h4 to h3.

And add this at the home's bottom:

"PrimeQA is a public open source repository that enables researchers and developers to train state-of-the-art models for question answering (QA). This page lets you try out sample demos of PrimeQA capabilities. Check out PrimeQA here: https://github.com/primeqa/primeqa".

Finally, render the selected collection's description under the select input on selection.