CLC-4221 - Create and deploy a mobile "home screen" icon for CalCentral

https://jira.ets.berkeley.edu/jira/browse/CLC-4221

We should do a lot of QA on this on multiple iOS / Android version and look specifically at the following areas:

* Log-in / logging out
* Updating the icon
* External links
* Performance (compared to the in browser experience)
* Font loading