add isValidTtl function

[bourgeoa]

This function is made to validate :

• any contentType/turtle
• if an .acl file has a valid acl content :
  . has a URI 'Control'
  . is the content structure valid with 2 options parameters :
  .. (with an options.aclValid to allow as a not blocking error with acl: Authorization missing)
  .. (with options.aclInherit to make it an obligation (to avoid a no access to the folder content))
  . each acl block should be composed of :

   :ReadWrite
  - acl authorization type
      a acl: Authorization
  - a combination of one or more agent/agentClass/group/origin
     acl:agent c:me;                           # agent
      acl:agentClass foaf:Agent;                # everybody
      acl:agentClass acl:AuthenticatedAgent     # logged in agent
      acl:agentGroup tes:this                   # group
      acl:origin <https://pod.solid.community>  # trusted app/agent bot
  - the accessTo resource
      acl:accessTo <${accessTo}>;
  - for a folder an acl:default 
      acl:default </>;
  - a combination of authorization : Read/Append/Write/Control
      acl:mode acl:Read, acl:Write.