Add appliance / incorrect file / Display both MD5 sum and file size

[scls19fr]

Hello,

I noticed that when you want to add an appliance which is an incorrect file the following message appears

This is not the correct file. The MD5 sum is a30bc9143788c76ed584ffd5d25fddfe and should be af4be6b27463446905f155f14232d2b4.
Do you want to accept it at your own risks?

In order to more easily fix appliance with new version this message should be better formatted and display both MD5 sum and file size (in bytes).

This is not the correct file.

MD5 sum
actual:   a30bc9143788c76ed584ffd5d25fddfe
expected: af4be6b27463446905f155f14232d2b4
File size
actual:   267386880
expected: 265186881

Do you want to accept it at your own risks?

This way it will be easier to provide new version for appliances

Kind regards

PS : could help fixing GNS3/gns3-registry#920

[grossmj]

Done, thanks 👍