添加修改内容是否保存的颜色标记(Change History Marker)

[Leroy-X]

在其他编辑器中，会用颜色标记出来修改但未保存或是修改后已保存的部分，标记颜色可以在主题中设置。 希望Notepad2添加类似的功能。 非常感谢！ Notepad++截图如下

[zufuliu]

Implemented by f69ab8b92dde9db24e879c3df381b5b1f74006bf. The marker is show on bookmark margin, global style "Change History Marker" set the color for saved (fore) and unsaved (back) changes.

This feature is disabled by default, quote from https://www.scintilla.org/ScintillaDoc.html#ChangeHistory:

This feature uses a moderate amount of memory proportional to the amount of modifications made. On huge documents, this could be significant so could be disabled when it would cause excessive memory use.

CC @xelsios, @VoilierBleu, @Matteo-Nigro, @maboroshin, @VenusGirl for translation updates (issue #886 has other changes).