replaced several calls to L::Local::find_home() with call to config instance; removed call to L::Local::Debug from lims_config.pl, as debug() uses config instance, which uses lims_config.pl; model classes get config from config instance instead of constructor passing it in LIMS::model(); general tidy-up
replaced multiple calls to load config settings with LIMS:Local::Config->instance(), using Class::Singleton to ensure config file opened & read only once at server startup
local changes for Bristol update: emailed messages contain test notice only if not in production; unreported requests worklist duration taken from config settings; config settings made available to Model classes; moved report output formatting to local template if not RR8
