Fixes for 5.1.2.
- Tapping the page counter no longer closes KOReader, with a wallpaper set (#436).
- The shelf follows a rotation you made while reading (#435).
- Spines keep their colour on colour screens (#430).
- The About screen no longer reports a second copy of Bookshelf when only one is installed.
- "Author on spine" can be turned back off (#439).
- A background no longer shows as a negative when night mode is set by a gesture or another plugin.