Feature/custom controller

[wenyuzheng]

What has changed

1. Add visible-to-admin-only controller html editor on project page, so only admins can see and upsert the html.
2. Add two admin-only controller html editor server functions: $getCustomControllerHtml and $upsertCustomControllerHtml. In the functions, getProject() is used to check if the project exists, this is to prevent a malicious projectId like ../../../ to escape the directory and access other directories.
3. Add three apis:

• POST /api/portal/v1/bind to bound the slide to the wall.
• GET /api/portal/v1/slides to get slides list of the current project and commit.
• GET /api/portal/v1/controllers/$projectId to serve the html file.

4. Add CONTROLLER_DIR to env and serverVariables so management centralised.