Support npm@5 and yarn (#6010)

* Support npm@5 and yarn

Use package.default.json
Partial #6008

- Overwrite package.json with package.default.json values
- `dependencies` field is merged with package.default.json version taking precidence
- `./nodebb upgrade` automatically does those things and runs `git pull`
- use `./nodebb upgrade --dev` to avoid the `git pull`

* added logic to preserve extraneous plugins installed in node_modules/

* Don't automatically git pull

* Simplify package-install, run it on upgrade just in case

nodebb

@@ -6,18 +6,20 @@ var fs = require('fs');
 var path = require('path');
 var cproc = require('child_process');
 
+var packageInstall = require('./src/meta/package-install');
+
 // check to make sure dependencies are installed
 try {
+	fs.readFileSync(path.join(__dirname, './package.json'));
 	fs.readFileSync(path.join(__dirname, 'node_modules/async/package.json'));
 } catch (e) {
 	if (e.code === 'ENOENT') {
 		process.stdout.write('Dependencies not yet installed.\n');
 		process.stdout.write('Installing them now...\n\n');
 
-		cproc.execSync('npm i --production', {
-			cwd: __dirname,
-			stdio: [0, 1, 2],
-		});
+		packageInstall.updatePackageFile();
+		packageInstall.preserveExtraneousPlugins();
+		packageInstall.npmInstallProduction();
 	} else {
 		throw e;
 	}
@@ -458,9 +460,15 @@ var commands = {
 			}
 
 			async.series([
+				function (next) {
+					packageInstall.updatePackageFile();
+					packageInstall.preserveExtraneousPlugins();
+					next();
+				},
 				function (next) {
 					process.stdout.write('1. '.bold + 'Bringing base dependencies up to date... '.yellow);
-					cproc.exec('npm i --production', { cwd: __dirname, stdio: 'ignore' }, next);
+					packageInstall.npmInstallProduction();
+					next();
 				},
 				function (next) {
 					process.stdout.write('OK\n'.green);