Hackage database support + fixes for Browser + Cabal files improvements

[serras]

With these commits, three different things are being worked on:

• there are some fixes for the Browser, mostly speed improvements. Now package information that cannot be gathered is blacklisted, until a new version of the same package is installed. Also, checking for Hoogle presence is much faster, which means faster startup times for EclipseFP.
• scion-browser was enhaced with support for downloading the entire Hackage database and browsing it. EclipseFP Hoogle and Browser views now support it. However, it's not used by default, as it uses about 1 GB of RAM. The user can select in the Preferences whether to use it or not.
• in the Project Explorer the Cabal file is shown first and can be expanded. I'm working on running executables, test-suites and benchmarks from there, but I hadn't had time to do it yet.