Add button to delete snippets

Description

User can now delete snippets they own. Also, users can delete snippets from organizations they are members of. Note: User cannot delete snippets if they are not logged in or do not own the snippet.

Motivation and Context

Fixes #413 branches off of #497, so that must be merged first.

Checklist:

[x] My code follows the code style of this project.
[x] I have added tests to cover my changes.
[x] All new and existing tests passed.

Browsers

[x] Chrome
[x] Firefox
[x] Safari
[x] Mobile:
[ ] Other:

Screenshots (if appropriate):

Enabled when logged in

screen shot 2017-05-15 at 15 48 56

Shows confirmation Modal

screen shot 2017-05-15 at 15 49 01

Shows snackbar when deleting

screen shot 2017-05-15 at 15 49 13

Shows snackbar when deleted

screen shot 2017-05-15 at 15 49 14

Delete is enabled for organization members

screen shot 2017-05-15 at 15 49 55

Not enabled on unsaved snippets

screen shot 2017-05-15 at 15 48 41

maryvilledev / codesplainUI

Add button to delete snippets #499