Updated contribution guidelines

We sadly still need to be more clear that tickets need to adhere to certain standards to be manageable...
Don't die if you're not able to log a print (e.g. for prints from SD)
Made "Streaming done" notification green
Generate the key used for session hashing individually for each server instance
Generate the key used for session hashing individually for each server instance
(cherry picked from commit 118a4f7)
Merge branch 'master' into devel

Conflicts:
	src/octoprint/server/__init__.py
	src/octoprint/settings.py
Allow login of the same user from multiple browsers without side effects

So far when logging in from two different browsers, then logging out in one of them the user was logged out across all browsers. This should now be changed in so far as that each individual browser session is tracked and only that session is ended by a logout that belongs to the browser where the logout button was clicked.

Should fix #556
Tornado's StaticFileHandler now supports content streaming, use that instead of our own implementation

Also allow for definition of access validation and serving as attachment though.

Hopefully also fixes #606, since that was possibly called by our own implementation of content streaming, which now has been removed completely.
Enable logging of tornado errors by default, to make sure octoprint.log will contain meaningful entries if something goes wrong in our tornado customization
Generate the salt used for hashing user passwords individually for each server instance
Merge branch 'master' into devel

Conflicts:
	src/octoprint/server/api/__init__.py
Preparing release of 1.1.1
Cura Plugin: Filament diameter and hotend temperature where not correctly extracted from profile and supplied to CuraEngine, resulting in low print quality

(using the default of 2.85mm filament diameter doesn't work well for 1.75mm machines...)
More work on slicing integration:

- be able to handle slicers which can't report progress
- distinguish between registered and configured slicers (e.g. to allow uploading of profiles via the settings before having saved the path to the executable)
Fix of file type detection
Fix: Don't try to create a SessionUser for anonymous users
Correctly interpret Smoothieware temperature data for multiple extruders

Fixes #633
Fix missing branch field in DEFAULT dict

Should fix an error raised on line 951 (SHORT_VERSION_PY % DEFAULT) during Octoprint setup when there's no version info. More info here: https://groups.google.com/forum/#!topic/deltabot/8udyUsJ1c9M
Request Settings data on opening modal

to counter different browser windows having different settings
Also interpret lines starting with "!!" as errors from the firmware

(see http://reprap.org/wiki/G-code#Replies_from_the_RepRap_machine_to_the_host_computer)