Fix job application spec formatting.

Refactor specs for Jobseeker#apply_to so that they describe the Jobseeker class, tweaking the strings so that the RSpec reports read more like natural language.
Add (fulfilled) multiple resume application spec.

Add (already fulfilled) spec confirming that jobseekers can apply to different jobs with different resumes.
Jobseeker: use JobApplier, fix #apply_to specs.

Refactor Jobseeker so that its instance of the new JobApplier class tracks the jobs to which it has applied and manages application validation for Jobseeker.

Update report specs to add required initializer parameters for Recruiter#post_job and Jobseeker#apply_to, using new parameter names.
Add other's resume submission failure spec.

Add spec checking whether a jobseeker cannot successfully apply to a job with a resume that belongs to a different jobseeker.
Fulfill wrong resume submission spec.

Fulfill spec confirming that jobseekers cannot apply to jobs with resumes that were created by other jobseekers.

Add Resume#belongs_to?.

Add WrongJobseekersResumeSubmission class.
Update interactions with feature addition.