Create hex color transformer
Decode hex color code in CETheme class
Use color code hex in CEThemeManager class
Migrate bundled themes to hex color code
Migrate theme to JSON format
Fix theme migration
Make sure unarchiving only color values in theme
Use NSCalibratedRGBColorSpace to store theme
Fix applying system selection color
Update WFColorCode to v1.1.1
Merge branch 'feature/readableTheme' into develop (See commit comment!!)

On this marge, the theme file format is changed to JSON + hex color code base. Remove all your customized themes in `~/Application Support/CotEditor/Themes/` before run this CotEditor. Sinse the theme integrated version of CotEditor has not been released yet, I did not create migration code for this change.