- Don't use `ioutil` package anymore as it doesn't anything special
anymore since Go 1.16:
```
// As of Go 1.16, the same functionality is now provided
// by package io or package os, and those implementations
// should be preferred in new code.
```
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
We have the `AppState` module now, it can store app related data easily. We do not need to create separate tables for each feature.
So the update checker can use `AppState` instead of a one-row dedicate table.
And the code of update checker is moved from `models` to `modules`.
