Use @uprtcl/evees in tests

[Pepo]

• instantiate an Evees service in the test
  • build a HtpSuperTest HttpConnection implementing the HttpAuthenticatedConnection interface.
  • create the HttpStore and EveesHttp services just like in Linked Thoughts app init.ts file
  • use the eveesConstructorHelper to build the evees service
• instantiate the AppElements service, giving it a tree of TextNode elements (instead of the custom types used in LinkedThoughts app) that are enough to run the test.
  • specify the tree structure with an AppElement similar to the app.element.init.ts file, just use TextNode as the only type of data to build the tree.
  • use elements.check() to intialize the tree.
  • use elements.get() to get elements inside the tree out of their "path".
• use the Evees service in the test to do some stuff. Create a perspective, update it, add a child...