plugins/netman: init + tests (#255)

Netman tests don't work if we try to effectively execute the config, so
a new parameter to `checkConfig` is introduced, `dontRun` that allows to
skip this phase.

plugins/utils/netman.nix

@@ -0,0 +1,29 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+} @ args: let
+  defs = import ../plugin-defs.nix {inherit pkgs;};
+  helpers = import ../helpers.nix args;
+in
+  with lib; {
+    options.plugins.netman = {
+      enable = mkEnableOption "netman.nvim, a framework to access remote resources";
+      package = helpers.mkPackageOption "netman.nvim" defs.netman-nvim;
+
+      neoTreeIntegration = mkEnableOption "support for netman as a neo-tree source";
+    };
+
+    config = let
+      cfg = config.plugins.netman;
+    in
+      mkIf cfg.enable {
+        extraPlugins = [cfg.package];
+        extraConfigLua = ''
+          require("netman")
+        '';
+
+        plugins.neo-tree.extraSources = mkIf cfg.neoTreeIntegration ["netman.ui.neo-tree"];
+      };
+  }