Fixed bug in host trace logging

Fixed bug in host trace logging

Trace macros in Ubuntu were not using the server context properly, so asserted after
65536 frames.

Added a getter to the stat-context-manager to get contexts by name, then utilized this
to add custom markers for tracing code.

(Trace macros are turned off by default, so they don't affect performance)

Enable by re-configuring with --enable-trace or gbs build --define "enable_trace 1"
in dali-core and dali-adaptor.

On desktop, also re-configure dali-adaptor with --enable-networklogging, and
run with DALI_NETWORK_CONTROL=3. Connect to the server using "nc localhost 3031"
and type "set_marker 131" to enable Update/Render/Custom trace.

On target, custom tags are sent to ttrace.

Change-Id: Iaff816f33c6c6034629759d1727a520a5cf5faf1
Signed-off-by: David Steele <david.steele@samsung.com>