Add Index on theme_settings.theme_id and theme_settings.setting_key to Accelerate Query

Created by: wtune

Problem

Missing index on table theme_settings column theme_id and setting_key might make the underlying query issued via ThemeSetting#findAllByThemeId&findByThemeIdAndKey slow.Since it's also easy to find that we always read theme_settings by setting_key or theme_id and sometimes insert or update, the performance impact for write operations is acceptable under common cases.

Possible Solution

Add Index on theme_settings.theme_id and theme_settings.setting_key