Add validation for JIRA Server field

[yannickoo]

This pull request adds a pattern and title attribute to the JIRA Server field so we can validate it when changing it's value. You can verify the RegEx here – it makes sure the server starts with http:// or https:// + some value after the protocol.

I also thought about using <input type="url"> but this requires more styling so I just added the pattern attribute for validation.

Wrong URL

Correct URL

This fixes #17 🔨

[iamJoeTaylor]

@yannickoo Thanks for submitting these. I'll try to take a look at these this weekend. It's been 4+ years since I looked at this code so I'll refamiliarize myself with it. Fun fact, my last commits were before I worked at Square, and now I don't work there again. :P

[yannickoo]

@iamJoeTaylor I also thought this project is abandoned and didn't expect a reaction 😅

I think this extension should be refactored to update the code style etc. but people are still using this extension since it's available on the Chrome Web Store.