[Mobile] Text annotation implementation has been completed.

[palahb]

Description: Text annotation implementation has been completed in the mobile app. A registered user is now able to create and view his/her text annotations in the application. Here are some screenshots of the feature:

Tasks Done:

• [x] Creating a page for text annotation creation
• [x] Creating a text annotation data model
• [x] Creating an API function for text annotation creation
  • [x] API function for annotation creation
  • [x] API function for getting previously created annotations of a post/article
• [x] Implementing necessary changes in the post and article reading pages:
  • [x] Adding textselection functionality to the post and article pages, adding annotation creation option
  • [x] Adding a section for seeing previously created annotations
  • [x] Creating a page for seeing previously created annotations

Reviewer: @enginoguzhansenol

Notes:

• Some packages needed version changes to implement this feature. To use this feature, please perform a pub get before using it.

Issue:

• See https://github.com/bounswe/bounswe2022group5/issues/459