Add/modify columns on customizable canvas

[chros73]

Add/modify columns on customizable canvas:

• override default Throttle column (⊘): display glyphs instead of the first character of the name of throttle
  • slowup throttle: ⊼
  • tardyup throttle: ⊻
• add back the removed Unsafe data column (◎)
• add back the removed Data directory column (⊕) (first character of parent directory)

Requires rTorrent-PS-CH 1.7.0 !
Refers to: chros73/rtorrent-ps-ch#119

You can also:

• disable default columns
• create your own columns