Make the git plugin look for the binary in the path specified in the settings. Previously, the environment was passed to the process, but that did not affect the location of the binary.

RevBy:    tba
Details:  - as on windows some git commands take much longer it happens fairly often, that git timeouts.
          - added a timeout value to the option to let the user choose maximum timeout value (minimum is 10 seconds, maximum 5 minutes)

replace ExtensionSystem::PluginManager::instance()->getObject<Core::ICore>() by Core::ICore::instance()

forward declaration is sufficient.

Details: Refactor the git command to be able to run a batch. Run diff and diff --cached in a batch