Guitar clone repos without submodules by default

[GermanAizek]

Example:

1. Clone https://github.com/mikex86/LibreCuda
2. Build failed

LibreCuda/third_party/ELFIO does not contain a CMakeLists.txt file.

LibreCuda/third_party/ELFIO really empty folder.

Solution: Experimental -> Submodule update...

@soramimi, by default, on contrary, everyone needs to clone recursively with update all submodules, and here it is just convenient to apply parallel cloning as in my other issue (#139)

[GermanAizek]

Larger git repos as example (https://github.com/shadps4-emu/shadPS4) are really cloned faster, although I forgot to do a fetch with -j flag, I will add PR later.

[GermanAizek]

Im added for git fetch: d6e2170