Switch to Python relative imports

When testing anaconda I discovered it doesn't work if it's directory is named `anaconda` instead of `Anaconda`.

The fix is very easy, so I decided to do it myself.

This change should not cause any errors.

One thing is still unresolved, though: hardcoded paths in anaconda's Sublime files (in `Main.sublime-menu`).
I have no idea how to fix them.