Issue 2147

[dqkqd]

This Pull Request fixes/closes #2147.

It will changes the following:

• [x] Disable edit [e] command when not at head revision
• [x] Add open [o] command to open the file if not at head revision
• [ ] Add go to head [g] command to jump to that file at head revision (If exist)
• [ ] Add proper error messages if tempfile cannot be created or opened ?
• [ ] Add proper error messages if go to head failed due to file is not presented ?
• [ ] Remove temporary file after close
• [ ] Add unittests

I followed the checklist:

• [ ] I added unittests
• [ ] I ran make check without errors
• [ ] I tested the overall application
• [ ] I added an appropriate item to the changelog