Add fallback to display line w/o column? Prio: line-column > line only

[DivineDominion]

line and column can be toggled on separately but are not used by the default themes.

Because of the performance problem reports pertaining column computation, I would suggest that this

(spaceline-toggle-line-column-on)
(spaceline-toggle-line-on)

Becomes a valid configuration in the default theme. Enabling only the column sounds less sensible, so this would be an opinionated configuration option.

In the rendition

 ((buffer-encoding-abbrev
        point-position
        line-column)
       :separator " | "
       :priority 96)

... line-column would've to be replaced with a function that uses line-column, and if that's nil, uses line` instead.

Before making a PR for this, I'd like to know if there's any interest in supporting this?

My rationale for suggesting this here instead of making the change locally: it's a shared perceived problem, and I would love to have more people adopt and stay with spaceline, even when they don't think they have the knowledge to do anything about the column performance issues.