Various fixes

* Protect __skrapport_*_style: macros
* Fix logic error in \__skrapport_email_list:
* Use \c_zero_skip instead of 0 in \__skrapport_pre_section:n
* Use \dim_set:Nn to set \hangindent, include box width inside
* Fix erroneous usage of non-existent \__skrapport_section_star:nnxxnn