Adapt process nice color according to definition

[nicolargo]

For the moment (Glances < 4.3), Glances display process nice level with the following color:

• not WARNING ==> COLOR_DEFAULT
• WARNING => COLOR_MAGENTA

WARNING can be defined in the Glances conf file (default WARNING: all but 0):

nice_warning=-20,-19,-18,-17,-16,-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19

We want 3 level according to nice definition:

NI -- Nice Value The nice value of the task. A negative nice value means higher priority, whereas a positive nice value means lower priority.Zero in this field simply means priority will not be adjusted in determining a task's dispatch-ability

So:

• 0 ==> COLOR_DEFAULT
• lower than 0 ==> COLOR_BLUE
• higher than 0 ==> COLOR_MAGENTA

[nicolargo]

Already done by conf