Convert to Rails 3.x / 4.x

[wtfiwtz]

This is a Rails 2.3.x style plugin... I have started converting it to a Rails 3 engine but have gotten stuck on how to get the Isolated Engine working correctly.

I'll send a pull request with a separate branch 'rails3'.

[cooperka]

Some resources I found to help:

• https://github.com/synbioz/odata_server/ has Rails 5 support incoming (via Rails 5 support synbioz/odata_server#1), new features and bug fixes
• https://github.com/timbogit/odata_server/commits/rails_5_2 has Rails 5 support (but the commit history makes it difficult to integrate changes back upstream)
• https://github.com/lmcalpin/odata_server has Rails 4 support