modify BackgroundFetchPlugin to run custom command
Submodule GitExtensionsDoc updated

Submodule GitExtensionsDoc:
    > 28e1384 - fixing Git Extensions and Git download link
    > d0dec73 - Adding troubleshooting section on mac installation
    > ac4a0c5 - Default clone destination. Closes #47.
    > c57ace3 - Version updated to 2.47
    > 2dd49d2 - Correction as per comment to PR#43.
    > 563780a - Commit font
    > 37e2e43 - Add new setting to Advanced->Confirmations
Text in AboutBox fixed
Problems with tranlation some items fixed
Russian translation updated
Correct refresh when another command than "git fetch"
Merge pull request #2052 from pmiossec/background_command

[Background fetch Plugin] Permit the user to run a custom fetch command