Add settings page with synced appearance and password change

- Store app settings as one JSON document on the server, merged per key and
  pushed to other devices; cache locally to avoid a flash on load
- Settings page groups appearance, account, shortcuts, shares, API tokens and
  trash; full screen with a section list on phones
- Font size and content width settings
- Change the login password, signing out other sessions
- Settings writes and password changes only accept a login session

internal/store/store.go

@@ -101,8 +101,9 @@ func (s *Store) DeleteSession(tokenHash string) error {
 	return err
 }
 
-func (s *Store) DeleteAllSessions() error {
-	_, err := s.db.Exec(`DELETE FROM sessions`)
+// DeleteOtherSessions 删除除 keepHash 之外的所有会话（修改密码后让其他设备重新登录）
+func (s *Store) DeleteOtherSessions(keepHash string) error {
+	_, err := s.db.Exec(`DELETE FROM sessions WHERE token_hash <> ?`, keepHash)
 	return err
 }