Add light and dark modes

[MitMaro]

Feature Request

Terminal emulators default to either a light background based theme or a dark background based theme. This tool assumes a dark background based terminal, but this isn't true for all terminals. For example the default terminal on Linux Mint:

It is currently possible to modify the colors to ensure that the text is visible on a white terminal, but it should be possible to switch the rebase editor to a light/dark mode that would provide a better set of defaults.

This should also be configurable via an environment variable, so that systems that switch light/dark mode based on the time of day can dynamically change the mode.

The color configuration should be updated to optionally take two colors per configuration.

[nickolay]

For me, on iTerm2 with the built-in "Light background" preset, the tool looks fine, except for the "selected" line, which is displayed as black-on-dark-grey. The only config that's needed to fix it is:

[interactive-rebase-tool]
selectedBackgroundColor = 240,240,240

UPD: https://github.com/dalance/termbg "A Rust library for terminal background color detection." might be useful.