Added button and modal framework for CSV download
Added interface to select streams for CSV file
Preliminary draft CSV Download feature; may have bugs, and may not behave cleanly for invalid input (e.g. no streams selected)
Cleaned up interface for selecting CSV files; added handling of error conditions
Update URLs; fixed conflict between background of stream tree and modal popup
Finished implementing CSV download
Merge branch 'csv-download' to make CSV download support mainstream

Conflicts:
	upmuplot/client/home.js