Inserting Snippets Anywhere

## Description
Insert snippets between any two snippets and before and after the automatic date headers by clicking the blue addition bubble that appears between snippets. 

Snippet deletion has also been rebuilt so that it all edge cases and cases that involve markers should be accounted for. Snippet addition has become easier since the only thing that is needed to be sent to the backend is the parent_id and then the service will automatically insert the snippet and reform the link list based on the id.

Marker-Group elements now are displayed between snippets that range more than five minutes rather than fifteen minutes. In this case there is one group element that is displayed when logged in as `test1@test.com`'s and in the philosophy 101 note.

Resolves #37 

### Testing Considerations
* [ ] Ensure a snippet can be added by clicking the blue addition bubble
* [ ] Ensure a snippet can be inserted as the first snippet
* [ ] Ensure snippets can be added before and after marker-day and marker-group elements
* [ ] Ensure snippet deletion works at edge cases and around marker day and marker-group elements
* [ ] Ensure snippet editing still works
* [ ] Ensure normal snippet addition through the writer still works