For projects with mandatory assignee use project lead

[codescape]

For mandatory assignee we can ask the ProjectManager, see:
https://docs.atlassian.com/software/jira/docs/api/7.1.5/com/atlassian/jira/project/ProjectManager.html#getDefaultAssignee-com.atlassian.jira.project.Project-com.atlassian.jira.bc.project.component.ProjectComponent-

Originally posted by @codescape in #15 (comment)

To be considered that an issue can be associated with multiple components and each component can define a default assignee. Use the first one? How does Jira itself deal with that?