Calabash inject dylib simulator

Support injecting libCalabash as a dylib and linking at runtime with lldb and dlopen.

See also: https://github.com/calabash/calabash-ios-server/pull/52


### todo

- [ ] expose `require 'calabash/dylibs'` as a top-level requirement after merging [PR #472](https://github.com/calabash/calabash-ios/pull/472)

That's correct, but it's is only a problem if you don't have Calabash installed and want to run "run_loop" stand-alone *AND* use the dylibs feature. 

Passing in dylib is the correct solution. I'm OK with merging this and fixing the issue in a separate pull request as this approach works fine in practice.