calabash backdoor should handle unrecognized selector without crashing the app

when passed an unrecognized selector, the server now replies with a dictionary populated with meaning values.  the details are, perhaps, a little too verbose but i wish there had been some examples/documentation for me when first started using calabash backdoor.

other changes:

#####  added `build` and `calabash.framework` to the .gitignore file
i think this makes sense, but i can understand that you might reject because of it.

##### updated the README.md file with steps for contributing to the 0.9.x calabash server
i think i got it right, but it could use some work.  reject if you must.

as for testing (always a pain on the server) i used the briar-ios-example 0.0.7 branch
git@github.com:jmoody/briar-ios-example.git
commit 249e7a33a0f1ca16ae12ce6e03b41426acf9a68c