Allow enabling/disabling uTP
Add utp option to SessionConfig + add to settingsdialog
Merge remote-tracking branch 'upstream/devel' into utp

Conflicts:
	Tribler/Core/defaults.py
Added CallbackConfigParser + SessionRuntimeConfig cleanup
Typo
Fix listen port config
Fix OperationNotPossibleAtRuntimeException at shutdown
Fix config_changed_callback return value
Merge pull request #307 from egbertbouman/utp

Allow uTP to be disabled
Merge branch 'devel' into issue296-2