Improve error handling for invalid setup for directory permissions

从 bin/lib/start.js 开始，然后沿着 lib/create-server.js、lib/create-app.js 和 lib/server-config.js 中的启动路径进行跟踪，尤其关注模板目录的初始化。使用一个无法创建的目录重现启动过程，并检查 EACCES 失败是如何报告的。完成标准是准确地呈现权限错误，而不是将其报告为 root 权限错误或端口错误。

When I started the server, I got this error:
ERROR You need root privileges to start on this port

It doesn't make sense because I wasn't running on port 80. So debugging it more (added console statements), I found that the true error was the following:

{ Error: EACCES: permission denied, mkdir '/var/www/solid.mysite/config/templates'
    at Object.fs.mkdirSync (fs.js:885:18)
    at mkdirsSync (/usr/lib/node_modules/solid-server/node_modules/fs-extra/lib/mkdirs/mkdirs-sync.js:31:9)
    at Object.mkdirsSync (/usr/lib/node_modules/solid-server/node_modules/fs-extra/lib/mkdirs/mkdirs-sync.js:37:16)
    at Object.copySync (/usr/lib/node_modules/solid-server/node_modules/fs-extra/lib/copy-sync/copy-sync.js:49:37)
    at ensureDirCopyExists (/usr/lib/node_modules/solid-server/lib/server-config.js:25:8)
    at Object.initTemplateDirs (/usr/lib/node_modules/solid-server/lib/server-config.js:108:29)
    at createApp (/usr/lib/node_modules/solid-server/lib/create-app.js:45:27)
    at Function.createServer (/usr/lib/node_modules/solid-server/lib/create-server.js:15:18)
    at bin (/usr/lib/node_modules/solid-server/bin/lib/start.js:122:17)
    at fs.readFile (/usr/lib/node_modules/solid-server/bin/lib/start.js:41:7)
  errno: -13,
  code: 'EACCES',
  syscall: 'mkdir',
  path: '/var/www/solid.mysite/config/templates' }

It should assist the user to fix their permissions not run it in root.