Fix local field validation
Catch assertion error from gitHub-flask library

The GitHub-flask library will raise an assertion error if GitHub returns
a status code that isn't 4xx or 2xx. This caused crashes when GitHub
returned a 503 error.

For now I'm just catching the error and reporting it. In the future I'll
probably submit a pull request to the library that makes it do something
more sensible.
Add more detailed error messages

The first flash is now treated like the title of the error message. Any
other flashes after it are treated like details of the error and put
into a bullleted list under the first message.

Also fixed an issue where messages would show side by side by putting a
<br/> after each message div. There's probably a better way of doing
this, but not one I know. My lack of CSS knowledge betrays me again...
Made the issue field larger

On some browsers the 'number' input type is rendered as a spinner. This
is great, except the spinner controls take up a lot of room, obscuring
the actual value in the field.

Making the box unnecessarily wide should fix this.