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)

@krukow 

This creates a dependency loop - calabash depends on run_loop and run_loop depends on calabash.

Does it make more sense to embed the dylibs in run_loop?  

Or change the arguments passed to run_loop from calabash to include the path to the dylib?

Instead of :inject_dylib passing a boolean - have it pass the path to the dylib to inject?