Changes for latest dc42 RepRapFirmware

Support long filenames
Sort gcode file list alphabetically
Use new Duet status response format
Recognize and display Halted state
Change icon colour
Update README.md
Update README.md
Removed reprap.remote.htm
Update README.md
Fixed bug with printing small files

Fixed bug that caused the interface to hang when trying to print a gcode
that was less than 21 lines long
Preliminary changes for file upload & print
Finished new upload & print function

Finished support for new button that uploads a file to a temporary file
name on the SD card and then prints it. The interface also remembers the
layer height of the last file it uploaded.
Update README.md
Merge pull request #9 from dc42/master

Incorporate dc42's latest changes into master