feat: split the folder actions out of the repository extension

Open Terminal Here and Open in Editor were bundled with git emblems, columns and a properties tab, but neither of them has anything to do with git and both work on any folder. They are their own plugin now, on the nemo-repo-core config and launcher layer.

The editor entry used to be shown only when Visual Studio Code was installed, whatever editor_command said; it now checks the configured command. The terminal entry is hidden when no emulator is present instead of appearing and doing nothing.

uninstall.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+# Removes this plugin from Nemo. The core, the other plugins and the config
+# file are left alone.
+set -euo pipefail
+
+dataHome="${XDG_DATA_HOME:-$HOME/.local/share}"
+extensionsDir="$dataHome/nemo-python/extensions"
+target="$extensionsDir/nemoFolderTools.py"
+
+if [ -e "$target" ]; then
+  rm -f "$target"
+  echo "Removed $target"
+else
+  echo "Not installed: $target"
+fi
+
+rm -f "$extensionsDir/__pycache__/nemoFolderTools".*.pyc
+
+echo
+echo "Restart Nemo to unload it:  nemo -q"