* tweak utils.Merge docs
* move merge_test to utils_test package for easier testing
* utils: support MergeConfig and StructFieldFilter
* constrain updating certain fields by the restricted system admin
* api4: break out license and config from system
* app: move some config functions from admin.go to config.go
* add ExperimentalSettings.RestrictSystemAdmin
* forbid various actions to restricted system admin
* update default.json
* fix function names in errors