[QA] Using all threads for most tasks

[GermanAizek]

@soramimi, thanks lot for really handy git client, I couldn't find replacement for GitExtensions on Linux and accidentally stumbled upon your project. But I use two CPUs and noticed that some very big projects with most submodules take a long time to clone. Do you use parameter '-j', '--jobs' with all system threads by default in all git operations?

Example on Linux: git clone --recurse-submodules -j$(nproc --all) https://github.com/soramimi/Guitar