Move API calls to separate files

[cojoj]

At the moment, all API calls are stored in XcodeServer.swift. It'd be advisable to move the to separate files and make extensions from them as the number of API calls may increase in the future.

I suggest separating them by type eg. XcodeServer+Bots will store all Bot related API calls, XcodeServer+Integrations will handle Integration and so on...

I don't know what's the proper naming convention and used well know convention from Objective-C. We can stick to this or decide on different style.

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This issue is blocked until #44 is completed as this one may introduce some merge conflicts.

[cojoj]

@czechboy0 please hold with work in XcodeServer class as I'm planning to apply proposed changes in this issue. I'll probably do it today.

It's already a pain in the ass working with XcodeServer class in #48 so it's high time to do some clean up! 😉

[czechboy0]

Go for it, I don't have any outstanding work on a branch (a rare moment, use it). I was working on Buildasaur the other day, migrating that beast to Swift 2.

[czechboy0]

Another one: #55.

[cojoj]

Platform and Device added here: #57

[czechboy0]

Finished by #58.