Feature/backend/annotations

[gumityolcu]

Summary of endpoints in this PR:

GET /api/annotation/:id Request: id is the mongo id.

Response: Annotation with the requested id is returned. id field in annotation is changed to URL.

GET /api/annotations?url= Request: Annotations on the webpage URL are given. Pagination is done via skip and limit query parameters. If omitted skip is assumed 0, limit is assumed 10.

Response: An array of annotations are returned, all having URL ids.

POST /api/annotations Request: no id should be given.

Response: id is URL.

PUT and DELETE /api/annotations: Request: id is mongo id.

Response: id is URL.

[nazmicancalik]

Awesome Job @gumityolcu 👍

[okyksl]

:)