Fix dev image

[ro-tex]

Our dev image doesn't work because siad needs glibc which is not available in alpine. But there is a workaround which is implemented here.

I am also piggy-backing a couple of minor updates on this PR:

• fixed the shape of the logo icon in the readme to have rounded corners and wrapped some long lines
• added an autoheal label to the alpine container as this was somehow omitted in the relevant PR
• added more informative logging to the build script, so we know which image failed to build without trawling through hundreds of lines of output
• removed the cleanup step in the build command because it was breaking Travis and it's generally not needed
• removed the hook that triggers a DockerHub build because we'll do it differently - DockerHub will monitor the repo directly