Remove the 'V' image from top-left of page
New: Files Are Filtered by Type and Extension when Selected

Previously, the Web App would allow users to upload any file. Now, only files
with the proper extension are allowed. Further, users are warned about files
with a proper extension but unexpected type.

Closes #33
Update minimum required 'vis-framework' version

In commit a1f0846e47baeaf0f63fd50f6f55a5fd6ca07266, having the CWA always use
WorkflowManager.output() instead of export() requires a version of VIS where
export() is deprecated.