Task #3292

Updated by Qiuhan Ding about 5 years ago

`TrustAnchorContainer` is a member of validator::KeyManager, which manages pre-trusted keys. 

 There are two types of pre trusted keys: `static` which once loaded will stay in the container forever, and `dynamic` which will be refreshed every certain period. 
 The dynamic keys can be reloaded from a file path. When the path points to a file, a key will be loaded from the file; when the path points to a directory, all the keys under the directory will be loaded.  

 TrustAnchors can be searched by key name, it can also be searched by group. Each group of dynamic keys are assigned an ID. For example, if all dynamic keys under a directory could be grouped together and share the same ID. 

     Code comes soon