Missing dependencies check

[Loki-Lokster]

Describe the bug
Currently there are no checks being made to see if a mod requires on other dependencies. This will become even more of an issue once KSP1 support is implemented.

To Reproduce

1. Download a mod that has other dependencies
2. Toucan will not notify you that you are missing dependencies
3. SpaceWarp modloader will then tell you in the main menu what you are missing

Solution
The creator of SpaceWarp has thankfully already implemented a simple system for mod authors to include mod dependencies within the swinfo.json file (thank you). We can utilise this to then check when a mod is downloaded if the dependencies have also been installed or not (and if they are up to date).