a spinner

[samuelcole]

fixes #50

[kahneraja]

have i got this right? When i attempt to load an invalid file the error doesn't show as expected.

this seems to be the case for both ?file=xxx.csv and ?externalFileURL=http://www.random.com/xxx.csv

master doesn't have this change and the error message loads as expected.

i'll add automated tests for this stuff asap.

[samuelcole]

ah yes! i forgot the error case

[alexyaseen]

+1