Feature/restrict query deletion

- The delete button now works!
- Only available to those with the permission to edit queries.
- Only deletes a query if it is not being used in a dashboard.
- Queries can be deleted from either /queries or /query/query_id
why the check against ` > -1`? 
So if your `currentUser.permissions` is set to `0` then you also show the delete column?
To be honest - my question is what kind of values would `currentUser.permissions` contain and what do they mean? Maybe adding a line or two of comments would make the code less obscure :wink: