Configurable buffer depths in CommandableFragmentGenerator
CommandableFragmentGenerator has event buffering capabaility in Buffered and Window trigger modes. This buffering should be tunable in terms of fragments and/or size.
Added the data_buffer_depth_fragments and data_buffer_depth_mb FhiCL parameters to CommandableFragmentGenerator. When running with separate_data_thread: true, if the buffers are full then further calls to getNext_ will not be made until the buffer drains.