USS Delete file/directory endpoint

[jordanCain]

There's currently no option to delete a unix file or directory

The solution for this would be the implementation of a DELETE endpoint that will delete the asset at the given path.

Original issue: #75

As a USS endpoint user
I want the ability to delete unix assets
so that I can delete files from the remote system

Acceptance Criteria

*Scenario 1: Delete unix asset
Given an existing unix asset
When I submit a DELETE request to the asset path
Then the file on the remote system is deleted

*Scenario 2: Delete unix asset that has a lock
Given an existing unix asset that is currently locked
When I submit a DELETE request to the asset path
Then the file on the remote system is not deleted
and appropriate response is returned