Support overriding diff options in project config (& for individual units) (#263)

* Support loading diff options from project config

* Support per-unit option overrides

Cargo.lock

@@ -1255,6 +1255,15 @@ dependencies = [
  "unicode-segmentation",
 ]
 
+[[package]]
+name = "egui-notify"
+version = "0.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3cd148c4c3fe05be0d9facf90add19a1531c1d7bfb9c7e4dbc179cfb31844d49"
+dependencies = [
+ "egui",
+]
+
 [[package]]
 name = "egui-wgpu"
 version = "0.32.3"
@@ -3564,6 +3573,7 @@ dependencies = [
  "dirs",
  "eframe",
  "egui",
+ "egui-notify",
  "egui_extras",
  "exec",
  "filetime",