add warning in Chrome when using file://

[notetiene]

Previously, there was a warning in Chrome about using the extension with the file:// scheme. Chrome doesn't support loading files from that scheme using XMLHttpRequest. Also, since the file input doesn't work anymore ( #21 ), it was a noisy warning I decided to remove.

Actually there may be a workaround by using the filesystem API, but injecting it might be much more complicated.

[notetiene]

This is now fixed in the Devel branch.

[Alleno]

This still appears to be a problem in the extension downloaded from chrome store. I've got it installed on ubuntu 16.04, and it doesn't seem to want to load tests from file. The two sample tests work though.