Add Web protocol to list directory structure on pvserver side

Extend Existing directory proxy to allow remote directory listing from Python.
Add web protocol for FileBrowser widget using that new directory listing proxy

Change-Id: If7d5de6d8a965d848f2a428c7e16652d45271552
Make sure to invalidate viewport when switching the active one

Change-Id: I561a5cf9a86b2ba1e2f0e8e08992ea1d6f7a49be
Bring WebGL fix

Change-Id: I368af6938b5e11b1a083a57dfdb29965b198025d
Merge topic 'pvweb-proxy-file-listing' into next

90afaa3 Bring WebGL fix
902deac Make sure to invalidate viewport when switching the active one
b72daab Add Web protocol to list directory structure on pvserver side