Ability to edit WP Job Manager Dashboard Navigation & Add Job Calendar to Dashboard.

### Is your feature request related to a problem? Please describe
When the plugin is used for websites where many ongoing jobs are being assigned to the same user, such as a gig site where 1 user can accept and do many jobs from different companies, a job calendar in the WP Job Manager Dashboard which collects all accepted/hired jobs would be very useful...

### Describe the solution you'd like
A job calendar in the User WP Job Dashboard would collect all jobs user is hired for. User can click add job to job calendar once they are hired. Each time a job is accepted, it can be added to the users job calendar. Simple and useful feature but does not exist. Also, the ability to customize the job dashboard navigation so that one would be able to add these features themselves.

### Describe alternatives you've considered
A list of hired and active jobs would also be helpful, but this should be in addition to the above request. Many websites focus on allow 1 user to apply and work multiple jobs. Your plugin is extremely limited as it thinks people still apply for 1 job and work 9-5 until they die. The world changed, so adjust your perspective to a more flexible function rather this limited thing... Everything a person needs to do with your plugin requires custom code, just allow features to be added or removed creating a more custom plugin. This would also increase your sales since people would pay for said flexibility and customization ability.

### Additional context
Please add the calendar and list of jobs user has been hired for / active jobs list..

Start by mapping the WP Job Manager user dashboard navigation and the data flow for accepted or hired jobs. Separate the requested calendar, hired/active jobs list, and customizable navigation into defined scopes. Done should include agreed requirements and working dashboard behavior for each selected feature.

Written by the indexing model from the issue text.