Added error information for CommitError

CommitError now contains and displays the error information.

```CommitError([edit interfaces ge-0/0/1],unit 2,Only unit 0 is valid for this encapsulation)```

The information is stored in the errs variable as a dictionary and can be accessed by key:

```
e.errs
{'source': 'dcd', 'message': 'Only unit 0 is valid for this encapsulation', 'bad_element': 'unit 2', 'severity': 'error', 'edit_path': '[edit interfaces ge-0/0/1]'}

e.errs['edit_path']
'[edit interfaces ge-0/0/1]'
```