common: Add CheckTemplates which checks all strings if valid templates
common: Template is a struct for state reasons
common: tests for NewConfigTemplate
common: ConfigTemplate.Process can in-place modify
common: properly replace user/builder vars
common: errors while processing
common: don't prepend '.' on keynames of template keys
common: key names prefer mapstructure tag
common: better docs for the TemplateCOnfig
common: step to process config templates