Add changelog property on relevant services

[rambobinator]

Regarding Appnexus documentation: https://wiki.appnexus.com/display/api/Change+Log+Services#ChangeLogServices-getdetails Relevant services are:

• insertion-order
• line-item
• campaign
• profile

I had to rename service parameter to _service since change-log endpoint use it as needed argument.

I also add profile property the same way to keep services creation on a single function instead of redefining class everywhere.

[coveralls]

Coverage increased (+0.3%) to 90.0% when pulling 0cbeba245929a08454181fd2bbc2dc98588f3c7a on feature/changelog into 8d6e389b2c511d598bddc0be7102cc5dddb3a284 on master.

[rambobinator]

@ramnes i made the changes

[ramnes]

@romas, can you please also add an example of usage inside the README? You can also change service to service_name there, on the custom representation code block.

[rambobinator]

@ramnes done

[ramnes]

Thanks!