Upgraded to MVEL 2.1.6.Final
Additional fix for ERRAI-646: Avoid resetting SSE channel every 60 seconds

- For SSE, we now send an empty JSON array as data every 45 seconds to avoid inactivity timeouts
- SSE support was removed from StandardAsyncServlet
Upgraded to MVEL 2.1.7.Final
Removed comment to deprecate FROM_UI because it turned out to be useful (see ERRAI-643)
Merge branch '2.4'
Move ProxyUtil to errai-codegen and reuse in ERRAI-277 fix