Update serializers to remove empty choices, provide default values for fields, and better indicate the field type when possible for OPTIONS requests and browsable API docs.

awx/main/models/inventory.py

@@ -734,6 +734,7 @@ class InventorySourceOptions(BaseModel):
     '''
 
     SOURCE_CHOICES = [
+        ('',       _('Manual')),
         ('file',   _('Local File, Directory or Script')),
         ('rax',    _('Rackspace Cloud Servers')),
         ('ec2',    _('Amazon EC2')),

awx/main/models/jobs.py

@@ -41,6 +41,7 @@ class JobOptions(BaseModel):
     job_type = models.CharField(
         max_length=64,
         choices=JOB_TYPE_CHOICES,
+        default='run',
     )
     inventory = models.ForeignKey(
         'Inventory',

awx/main/models/projects.py

@@ -203,6 +203,7 @@ class Project(UnifiedJobTemplate, ProjectOptions):
     )
     scm_update_cache_timeout = models.PositiveIntegerField(
         default=0,
+        blank=True,
     )
 
     @classmethod