Implemented basic events.

The Torrent class now has a callback method to which you can assign to.
It's called everytime a change occured in the torrent state, could be useful for
example to send a notification to the user when a torrent finishes.
Merged wip/torrent-event in master
Better events
Move UI settings out of core
Sane size conversion
Fixes #108, #109
Remove useless things
Merge pull request #100 from lluixhi/master

Handles magnets and http links to torrent files.
Merge pull request #111 from fuyukaidesu/master

Events.
Update Platform_linux.cpp
Merge pull request #113 from gtorrent/clean-a-thing

\>having a development environment where using github's shitty online editor is easier than opening a separate terminal to do a two line edit
all -> system
only install what is needed
remove some lines & libtorrent-rasterbar-dev
Merge pull request #114 from gtorrent/does-this-even-build

travis build time cut in half
Remove verbose output
Support opening sub folders in Platform