Add a UI to the Windows installer

We'll be able to control whether the app starts up or not after
installation.
Switch license file to rtf and to the right license
Merge tag '4.1.0' into windows-installer-ui

4.1.0
Update license reference
Rename old service checks to network check
Update change log
Reorganize imports
Finish rename
Merge branch 'windows-installer-ui' into rudy/windows-cleanup
Windows| Make sure we don't bundle numpy
Windows| Rename servicechecks to networkchecks for windows
Windows| Add Mesos & Marathon to the checks not supported on windows
Windows| Dynamically set a junk img_path for spyderlib

py2exe bundled spyderlib can't access the usual image_path
It may be solved by modifying setup.py but this would be more
complicated and we don't use spyderlib's image resources anyway
Remove unused vars. Logs guilty stuck check.
Break after restarting pool because jobs_status is flushed
Windows| Fix tornado verison in requirements.txt
Merge pull request #1061 from DataDog/leo/unused_vars

Improvements on NetworkCheck class
Couchdb is started when installed by apt
We don't need that anymore with the self contained agent
The forwarder should always be running so there is no need for the emitter to support proxy connection anymore