Group/project members - migrate to namespaced Vuex modules

Summary

As a step in moving towards one Vue/Vuex app that uses GlTabs we need to convert the project/group members app to use namespaced Vuex modules. The modules will be user, group, invite, accessRequest.

Improvements

Allows us to move to one Vue app and migrate to GlTabs

Risks

Minimal, this is a well tested section of the codebase

Involved components

• app/assets/javascripts/members/components/modals/remove_group_link_modal.vue
• app/assets/javascripts/members/components/table/expiration_datepicker.vue
• app/assets/javascripts/members/components/table/members_table.vue
• app/assets/javascripts/members/components/table/members_table.vue
• app/assets/javascripts/members/store/index.js
• app/assets/javascripts/members/index.js