Add an available storage verification

[Nikki-Devil]

Adding a capacity storage check for the drive used to install Medicat would help prevent some weirdness (yeah some of us are dumb enough to not check the size of the tools they wanna use ^^")

Also, an available storage check when downloading via the installer would be helpful to prevent overloading the drive where the script runs

[David-Prock]

If for some reason you can't get the free space, if a format is going to take place, ignoring existing data, you could look at sectors/blocks go get a good idea/do the math.