Also allow downloading .g files via Tornado

Regex so far only matched .gcode and .gco, files ending just in .g are expected for upload as well though, so this needed to be adjusted
Merge branch 'master' into devel

Conflicts:
	src/octoprint/server/__init__.py
Fix: Use event strings, not names for all_events

Temporarily broke event registration by frontend, this should fix it again.
Merge branch 'devel' into dev/newFilemanagement
More work on new file management and slicing mechanic
Fix: gcodeFilesViewModel doesn't exist as invididual variable anymore, iterate over registered view models instead
Merge branch 'devel' into dev/newFilemanagement