Generate invite tokens from admin-fe

This MR allows to create invite tokens, list them on a separate tab, invite users via email. It also updates error handling and allows to generate tokens for resetting password.

Closes #28 (closed)

src/components/LangSelect/index.vue

-<template>
-  <el-dropdown trigger="click" class="international" @command="handleSetLanguage">
-    <div>
-      <svg-icon class-name="international-icon" icon-class="language" />
-    </div>
-    <el-dropdown-menu slot="dropdown">
-      <el-dropdown-item :disabled="language==='zh'" command="zh">中文</el-dropdown-item>
-      <el-dropdown-item :disabled="language==='en'" command="en">English</el-dropdown-item>
-      <el-dropdown-item :disabled="language==='es'" command="es">Español</el-dropdown-item>
-    </el-dropdown-menu>
-  </el-dropdown>
-</template>
-
-<script>
-export default {
-  computed: {
-    language() {
-      return this.$store.getters.language
-    }
-  },
-  methods: {
-    handleSetLanguage(lang) {
-      this.$i18n.locale = lang
-      this.$store.dispatch('setLanguage', lang)
-      this.$message({
-        message: 'Switch Language Success',
-        type: 'success'
-      })
-    }
-  }
-}
-</script>