Mapping Override Feature with Example Theme

- implemented ability to define mapping overrides in theme specification files
- added new example theme that uses the new function "Sublime Text Monokai Extended"
I removed the static because the parseTheme function ColorThemeManager.parseTheme function is not static and to me it seems to be difficult to make them static. Maybe you have a better understanding of the whole thing and can make it static. I tried to keep changes small.