Prototypic bundler-integration for Stickler

This is a rough attempt to solve #13 and get the required gems from bundlers Gemfile by iterating trought the list of all dependencies. It might be useful to migrate repositories to a internal Stickler-server or to keep mirrored gems up to date via "bundle update + stickler bundle".


### Example run
```bash
$ stickler bundle
Asking http://127.0.0.1:6789/ to mirror rspec-2.12.0 from rubygems.org : OK -> http://127.0.0.1:6789/gems/rspec-2.12.0.gem
Asking http://127.0.0.1:6789/ to mirror webmock-1.13.0 from rubygems.org : OK -> http://127.0.0.1:6789/gems/webmock-1.13.0.gem
Asking http://127.0.0.1:6789/ to mirror vcr-2.5.0 from rubygems.org : OK -> http://127.0.0.1:6789/gems/vcr-2.5.0.gem
Asking http://127.0.0.1:6789/ to mirror uglifier-2.1.2 from rubygems.org : OK -> http://127.0.0.1:6789/gems/uglifier-2.1.2.gem
Asking http://127.0.0.1:6789/ to mirror tzinfo-0.3.37 from rubygems.org : ERROR: gem tzinfo-0.3.37 already exists in remote repository
Asking http://127.0.0.1:6789/ to mirror treetop-1.4.14 from rubygems.org : ERROR: gem treetop-1.4.14 already exists in remote repository

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