[IP-X] Module for managing cars in Invoiceplane

[AndyX90]

I don't know if this project is already dead, but here is my first module for managing Vehicles.
You can add Cars, assign them to Clients, Quotes, Invoices..

Pull Request Checklist

• My code follows the code formatting guidelines.
• I have an issue ID for this pull request.
• I selected the corresponding branch.
• I have rebased my changes on top of the corresponding branch.

Issue Type (Please check one or more)

• Bugfix
• Improvement of an existing Feature
• New Feature

[UnderDogg]

@AndyX90 the project isn't dead and thank you for the pull request. Would you like to join our slack and help develop on the project?

[AndyX90]

@UnderDogg Yes, thank you!

[UnderDogg]

We're having our slack at invoiceplane.slack.com (I couldn't send you a PM)
I've set the base for your PR to a different branch and found 4 conflicts, mostly because of other PR's in that branch.
Let's see if those conflicts can be fixed easily