Persist column widths across sessions

[matthew-matvei]

Feature

The width of the columns are now dynamic. It would be more useful to the user for them to be persisted across sessions so that once a suitable width has been found, this will be used the next time the app is opened. This should be configurable in the same way that preserving window and pane dimensions is.

• Column widths stored per pane on end of width change

Proposed solution

The Persister class should be able to handle storing column widths.