Site changes are not reflected when fetching it on app launch

[hichamboushaba]

Currently, the selected site is cached in memory in SelectedSite, and when the app refreshes the site information on app launch (and when resuming from background), we don't update the in-memory version, which requires force closing the app and relaunching it to pick those changes.

• We need to ensure that we update the site after fetching it.
• Look into implementing equals on the SiteModel to avoid useless notifications to the observers.

[dangermattic]

🚫 Please add a type label (e.g. type: enhancement) and a feature label (e.g. feature: stats) to this issue.