fixed some of the attribute access exceptions in 'symbols.py' and restored panel 'select imported module'

I tried to fix some of the errors i get with the last version of sublimeHaskell plugin installed on my ST3. I found that some fields and functions in 'symbols.py' seemed to be removed already yet still tried to be accessed, throwing exceptions and preventing 'Show symbol info' option working correctly.

(+) Additionally i discovered, that the panel for selecting from the list of imported modules was not displayed properly. I fixed that too.