Remove duplicate bootcamp information

For some reason some bootcamps have been duplicate in
`config/bootcamps_saved.yml`.

This commit remove all duplicate bootcamps.

~~~
$ grep slug config/bootcamps_saved.yml | wc -l
136
$ grep slug config/bootcamps_saved.yml | sort | uniq | wc -l
136
~~~
1. Integrated @r-gaia-cs's fix for duplicated bootcamp URLs.
2. Adding script to check for reoccurence.
3. Renaming Makefile targets: `make site` now builds locally for checking (as it does with `bc`), and `make check` checks validity of metadata.
Merge pull request #391 from gvwilson/remove-dup

Remove dup