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
@krukow 

Can we remove the CALABASH_USE_DYLIB variable and just rely on the :inject_dylib argument?

The environmental variables are difficult to maintain, document, and deprecate.