Remove deprecated models and mobx usage (react-query refactor) (#1934)
* Update login page to use service query
* Update modal to use session instead of store
* Move image sizes cache off store
* Update settings to no longer use store
* Update link-meta fetch to use agent instead of rootstore
* Remove deprecated resolveName()
* Delete deprecated link-metas cache
* Delete deprecated posts cache
* Delete all remaining mobx models, including the root store
* Strip out unused mobx observer wrappers
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