Linux/mac fix for setup

[mallewellyn]

This definitely needs looking at/tested, especially on Mac. I tested on Linux and it seems to work and removes igraph/minfi issues.

To explain PR:

• Because the second link in Error in Linux setup #160 requires a mixture of R and bash to install dependencies, it could be easier to use the first link and require all system dependencies are installed. Checked the latter and the dependencies don't seem to take too long to install. Could replace the Linux caveat (currently about igraph) with something similar to the code I've proposed.
• Tested on Ubuntu without any problems and seems to resolve igraph issue. I actually don't know that the Ubuntu code can be used on Mac as stated in this new version so will need to be tested/checked (my understanding is that the Mac terminal uses bash?).