Improve detection of default external terminal on linux
Make use of the new pyqode-console wrapper

This fix issue #68 on linux only (I will have to test that on windows and mac)
This will also help to avoid issue like #71
Fix opening of file where encoding detection failed

Now the editor will show up with the encoding panel visible so that user can reload the editor with another encoding

This commit also fix the encoding cache issue on the cobol backend