Fix broken links and update the README.md file

[mdew192837]

• Removed Jenkins Cloudbees (No longer in use)
• Deleted Reference Client App Link (broken and deprecated)
• Updated links for the developers, platform implementation, and git sections
• Updated link for the demo video
• Improved the wording and grammar
• Removed target='_blank' as that is not supported
• Enclosed bare links in <> specified by Markdown language

You can preview the new implementation here: https://github.com/mdew192837/mifosx/tree/FixBrokenLinks

[mdew192837]

I'm not sure why the tests are failing. It says it is due to no rake file. I don't think that's related to me though.

[nazeer1100126]

@mdew192837 This repository is not active. Please send PR to https://github.com/apache/incubator-fineract