Impl get_status

[elpiel]

Resolves https://github.com/AdExNetwork/adex-market/issues/5

• [x] #6 enum Status
• [x] #6 fn get_status
  • [ ] test
• [x] #6 fn is_finalized
  • [x] #10 test
• [x] #7 fn is_date_recent + testing @simzzz
• [x] #7 fn is_initializing + testing @simzzz
• [x] #6 fn is_offline
  • [x] #10 test
• [x] #7 fn is_disconnected + testing @simzzz
• [x] #17 fn is_rejected_state + testing @simzzz
• [x] #17 fn is_unhealthy + testing @simzzz
• [x] #20 fn is_active + testing @simzzz
• [x] #20 fn is_ready + testing @simzzz

[elpiel]

Additional check was added (that exists in JS) in PR https://github.com/AdExNetwork/adex-supermarket/pull/37 for channel_active_from when evaluating the Active & Waiting statuses

This still needs tests for the get_status function itself