Fix IllegalArgumentException when using navigation up buttom in SettingsActivity

Due to 5b9bf430955dbd70ccd98b61ed05664c72e69d18.
Support adding thread to favourites

* Use `LoaderDialogFragment` instead of `LoaderFragment` to wrap `Loader`
Rename variables and add blank line to `dialog_seekbar.xml`
Tweak `ImageTagHandler` and support image url copy when selected
Support <strike> tag for post