refactor: grade --> grade (1/2)

Rationale: `grade` comes from a frencophone bias.

openapi/components/schemas/ballot.yaml

@@ -5,7 +5,10 @@ properties:
     description: A unique identifier
     example: 4
     readOnly: true
-  mention:
+  grade:
     type: integer
-    description: The mention item, according to the mentions array defined when creating the poll.
+    description: >
+      One grade of the grading defined when creating the poll.
+      Zero (0) means the worst grade, and it goes upwards from there,
+      up to the size of the grading, minus one.
     example: 2

openapi/components/schemas/mention.yaml

@@ -2,16 +2,19 @@ type: object
 properties:
   id:
     type: integer
-    description: A unique identifier
+    description: >
+      Unique identifier of the grade in its grading.
+      Zero (0) is the worst grade, and it goes upwards.
     example: 0
     readOnly: true
   name:
     type: string
-    description: Unique but short name of the mention, like *Excellent* or *To reject*.
-    example: Excellent
+    description: >
+      Unique but short name of the grade, like "Excellent" or "To reject".
+    example: Good
   description:
     type: string
-    description: An optional description of the mention
-    example: In this poll, the mention *To reject* disqualifies the proposal.
+    description: An optional description of the grade.
+    example: In this poll, the grade "To reject" disqualifies the proposal.
 required:
   - name

openapi/components/schemas/poll.yaml

@@ -2,7 +2,7 @@ type: object
 properties:
   id:
     type: string
-    description: A unique identifier
+    description: A unique identifier.
     example: 1jDe1e5eF_IkaYPuoIYX
     readOnly: true
   title:
@@ -12,7 +12,7 @@ properties:
   description:
     type: string
     description: A description of the poll
-    example: 
+    example:
   proposals:
     type: array
     description: The proposals being voted in a poll.
@@ -20,13 +20,13 @@ properties:
     maxItems: 20
     items:
       $ref: ./proposal.yaml
-  mentions:
+  grades:
     type: array
-    description: The mentions on which one participant vote to a proposal.
+    description: The grades on which one participant vote to a proposal.
     minItems: 2
     maxItems: 10
     items:
-      $ref: ./mention.yaml
+      $ref: ./grade.yaml
   participants:
     type: array
     description: The participants that are allowed to participate to the election.
@@ -37,7 +37,7 @@ properties:
     description: Organizer id. If not given, a dummy user is created.
   restrict-participants:
     type: boolean
-    description: True if anyone can participate to this poll, False otherwise.
+    description: True if anyone can participate in this poll, False otherwise.
     example: false
 required:
   - title

openapi/components/schemas/result.yaml

@@ -4,8 +4,8 @@ properties:
     $ref: ./poll.yaml
   ranking:
     type: array
-    description: An array representing mentions level for each proposal,
-      according to the mentions list, following the order of the proposals array
+    description: An array representing grades level for each proposal,
+      according to the grades list, following the order of the proposals array
       defined when the related poll has been created.
     example: [0, 6, 3, 2, 2]
     minItems: 2