Display documents

Initial main frame which holds the filemenu, report, and results panel
Can currently switch focus documents by selecting a report from the list.
Reports are probably going to be json, html, or xml
May wish to use a constant at the top of accepted report formats
```python
REPORT_FORMATS = ['.xml', '.json']
...
if os.path.isfile(f):
    if os.path.splitext(f)[1] in REPORT_FORMATS:
        # stuff
```