[web] Documentation for line source terms.

...nd_simulated_temperature_line_source_term_in_cylinder.png

...nd_simulated_temperature_line_source_term_in_cylinder.png

...temperature_line_source_term_in_axisymmetric_cylinder.png

...istribution_line_source_term_in_axisymmetric_cylinder.png

...temperature_distribution_line_source_term_in_cylinder.png

...ure_profile_line_source_term_in_axisymmetric_cylinder.png

...ures/temperature_profile_line_source_term_in_cylinder.png

...rks/heatconduction/heatconduction-line_source_term.pandoc