pSTIR.ListModeToSinograms.set_template from ProjData

[evgueni-ovtchinnikov]

LmToProjData.post_processing() fails if template_proj_data_name is empty, which prevents the resolution of SyneRBI/SIRF#173

[KrisThielemans]

This is addressed in #828 by splitting functionality to set_up(). It will mean that SIRF will have to call set_up() once merged (to release_4 and master).