Energy resolution units for sinogram header

[emikhaylova]

When using "create_projdata_template", one of the questions is:
Enter the energy resolution of the scanner : [0,1000 D:-1]:
What are these units?

[KrisThielemans]

From the following, it follows that Scanner::energy_resolution is expressed as a fraction (and computed at the reference energy), so should be between 0 and 1.

STIR/src/scatter_buildblock/scatter_detection_modelling.cxx

Lines 117 to 118 in e0e40a9

	sqrt(2.*energy*this->proj_data_info_cyl_noarc_cor_sptr->get_scanner_ptr()->get_reference_energy())*
	this->proj_data_info_cyl_noarc_cor_sptr->get_scanner_ptr()->get_energy_resolution()/2.35482f; // 2.35482=2 * sqrt( 2 * ( log(2) )

This isn't documented, and in some places the doc seems actually wrong. PR in construction.

[KrisThielemans]

fixed by #1149