For each submodule native git allows to configure which modifications to
submodules should be ignored by the status command. It is possible to
ignore "none", "all", "dirty", "untracked" [1]. This configuration is
now supported by IndexDiff. The StatusCommand offers the possibility to
specify this mode.
[1] http://git-scm.com/docs/gitmodules
Change-Id: Ifd81d574a680f9b4152945ba70f8ec4af4f452c9