Evas/cserve2: Merge branch 'devs/jpeg/cserve2'

Improve stability, performance and overall support of
evas cserve2.

In particular:
- Implement shared indexes and memory pools to share cserve's
  internal state with all clients. Apps can then scan these
  indexes and avoid waiting for socket responses when loading
  resources.
- Implement crash resiliency in evas. If cserve2 crashes, apps
  can safely reconnect and continue working as if nothing
  happened.
- Implement support for the GL engine (very basic support so
  far, "just works").
- Improve performance by reusing the scalecache logic.