Added some tag & comment functionality

I resolved the merge conflict I was having last night YAY!! I closed the previous pull request, and this one is ready to be merged when someone gets a chance to review it.

Updates:
- Make tags clickable on index and built out tags show page
- Add tags field to new post and edit post pages
- Build out posts show page with date, tags, and comments
- Start building out comment functionality with comments show page
- Make sample about page