Sort process list on any column

[Atoptool]

Allow the process list to be sorted on any column in the current view, ascending or descending.

[Atoptool]

The process list can be sorted now on any column: with the key 'O' a column name can be entered (case insensitive) that is part of the current process view, either visible or invisible (when screen is too narrow). Furthermore a choice can be made to sort ascending or descending. The current sort column (if visible) will be highlighted.

For compatibility, the existing keys C (CPU), M (MEM), D (DSK), N (NET) and E (GPU) can still be used as shortcuts for the resource utilization column.

Notes:

• The key A (automatically sort on the most utilized resource) is not supported any more.
• For cgroups (shown by key G), sorting is still allowed for CPU utilization (C), memory utilization (M) and disk utilization (D), but not for other columns.

This modification also solves the issues #169, #301 and #305.