Make datatables server side. Kitchen sink commit.

* Update `jquery-rails-datatable` gem (which is my fork) with updated upstream Bootstrap plugins (fixes alignment issues on sort buttons)
* Change resource to `bikeway_segments`. This makes paths work as expected. Can't use different model/controller names if we expect Rails path magic to work!
* This means we had to rename a bunch of stuff, and unfortunately I didn't do it the Git way. Oh well.
* I felt dirty writing `BikewaySegmentDatatable`, because of all the Hungarian notation, and the complete utter lack of DRY. Having to specify my columns in order not once, not twice, but thrice, ick. Good thing this is just "admin" code.