Fix existing glitches

* Casting types
* "create" instead of "submit" in permissions
* Backlog items now have a project reference
* Backlog items and Milestones have now a tracker reference in "parent"

Change-Id: Ib98005c7a8dccc01db5c3e59c7673790985d31ee
Cast values, takin in account null cases

Change-Id: I193ae043cc833b34b2f52b40f64b8b418e30d174
Add tracker reference in artifact references

Change-Id: I0d5f066016cd463cdad0e33c1b35ad019fe8067d
Remove tracker field because it's already present in artifact
representation

Change-Id: Ib7b1c0a256c1d493b0c372302a38e12e62afe8f3
Throws 404 even if user is site admin

Change-Id: I5a2e012a0b92cd4e44a415c270247ac4302428f9
Fix milestone representation

* Added backlog_uri and content_uri
* Fix start_date, end_date and capacity values

Change-Id: Ib704cb36811117e37babcaf4d070034fe5c6e9bc
Merge "Remove tracker field because it's already present in artifact representation" into 5590_existing_glitches_to_be_fixed
Merge "Fix milestone representation" into 5590_existing_glitches_to_be_fixed
Add last_modified_date attribute

* ArtifactRepresentation
* MilestoneRepresentation

Change-Id: Ic9e0786a64cfe479a1b25254307e8319bc569a39
Display all available subresources of /projects/:id

Change-Id: I0fc9d2c9fb3736eee4a66f523d68af48d541425f
Merge "Display all available subresources of /projects/:id" into 5590_existing_glitches_to_be_fixed
Merge remote-tracking branch 'gerrit/5590_existing_glitches_to_be_fixed' into stable

* gerrit/5590_existing_glitches_to_be_fixed:
  Display all available subresources of /projects/:id
  Add last_modified_date attribute
  Fix milestone representation
  Throws 404 even if user is site admin
  Remove tracker field because it's already present in artifact representation
  Add tracker reference in artifact references
  Cast values, takin in account null cases
  Fix existing glitches

Change-Id: Iea57e687fe77e4dbf43715bfc399f67ce67cce6d
This is Tuleap 6.7.99.33

Change-Id: Iae878c2d540ba148e243217e36c0a567a2c5a449