`Return` key does not work for file loading/ state file download

[huiwanpnnl]

When I choose connectivity/simulations files to load or when I attempt to download a state file, the blue Load files and Download buttons work when I click on them but not when I press the return key on the keyboard. Could we allow the return key to work? Thanks!

[jourdain]

done in #87

[huiwanpnnl]

I tested v2.6.3 both at NERSC and on a MacBook Pro, and I confirm that this has been fixed in v2.6.3.