Merge pull request #2497 from RosettaCommons/vmullig/thread_efficiency_incremental_merge_1
Incremental merge of thread efficiency tweaks
Merging some of the changes from pull request #2479, since some of the other changes that are planned might take longer. This removes mutexes from core::chemical::ResidueProperties::get_variant_type_from_string() and core::chemical::ResidueProperties::get_property_from_string(), converting the relevant maps to const static data.