#1432 Improvement for the Open File List plugin

[benblan]

The open file list plugin could have the following improvements :
- customize the sort used to display the list (using the order of the editors or by name, ASC or DESC)
- display file with their relative paths to be able to distinguished between two files with the same name (sometimes the path is displayed and sometimes not)
- Display a customizable number of closed files directly in the same windows and not having 2 separates windows. Display the closed files in a second tree and different color for example.