Fetch home in background to cache messages

...main/java/app/fedilab/android/mastodon/helper/Helper.java

...va/app/fedilab/android/mastodon/jobs/FetchHomeWorker.java

...pp/fedilab/android/mastodon/jobs/NotificationsWorker.java

...todon/ui/fragment/settings/FragmentHomeCacheSettings.java

...odon/ui/fragment/settings/FragmentSettingsCategories.java

app/src/main/res/layouts/mastodon/values/strings.xml

app/src/main/res/navigation/nav_graph_settings.xml

app/src/main/res/values/strings.xml

app/src/main/res/xml/pref_categories.xml

app/src/main/res/xml/pref_home_cache.xml