Merge pull request #10 from danbender/comments

Comments
dan/ken: moved flash_error partial to layouts/
ken/dan:
* refactored the attach listeners function to follow single responsibility
* fixed strong params bug
dan/ken:
* when successfully creating a source redirect to root_path
* else render flash_error and redirect to new_source_path
ken/dan:
* create migration for comments
* set up comment model
* create associations between sources and comments
dan/ken:
* guest can add comment
* nested comments routes within sources
* all tests pass