[LIVY-409] Livy shell UX improvements
[LIVY-409] Livy shell UX improvements

I'm not sure how large of an audience the livy-shell has, but I've come to use it quite a bit in my testing/use of Livy and added a few small improvements that have made it a bit easier to use for me (and may help others):

* Replaced the use of httplib with requests to fix dropped connection issues (and a few other robustness issues).
* Added some context to the REPL prompt, by including the session `kind` and ID.
* Ignore `SIGINT` signal so that users can type `CTRL-C` to cancel out a command.

I know the use of `requests` is pretty ubiquitous but I included `livy-shell-requirements.txt` just in case 1) someone doesn't have it installed or 2) more dependencies are added down the road.

Author: Eric Perry <eric@ericjperry.com>

Closes #55 from ericjperry/feature/livy-shell-improvements.

ajbozarth/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy