gltrace: add user settings to control data captured.

Currently users do not have control over the amount of data
captured during tracing. This patch adds 3 settings that users
can enable/disable at runtime:
  - capture framebuffer on eglSwap() calls
  - capture framebuffer on glDraw*() calls
  - capture texture data passed to glTexImage*() calls
Disabling these options when not needed signficantly decreases
the size of the trace file, and reduces performance overhead for
the running application.

These settings are stored in the per process GLTraceState.
A separate thread listens for commands from the host, and updates
the state based on the user commands.

Change-Id: Ic4518b94e8bcbc5330ac7138153721caa98b365d