Support adding JARs from the libraries folder and the code folder
The code folder requires "code" and "code-dex" (which contains a dexed
version of the same files). Similarly, each library in the libraries
folder (like the one from the desktop, in the Sketchbook), must have a
"library" and "library-dex" folder. At present, only one JAR file per
library is supported, and natives aren't supported - I should get around
to fixing this. Additionally, there is no way to install the libraries
yet, but they can be placed in the libraries folder manually. Tested
with Ketai.