Theme: Organization of Notes

Description: After having the basic functionality of the note-taking feature (add and view notes), we need to have a folder system to group the notes and a filtering system to better organize the notes. This will allow the user to classify their notes so as to access the notes they want

Work distribution: Shonn will prioritize the xmls of the new activities and other attached items. Insung will prioritize writing functionality in Kotlin files for the new features and updating the database access. Kevin will prioritize the unit tests and ensure the working relations between xmls and Kotlin files.

Main target:

1. implement a working folder system: folders of different courses.
2. implement a working filtering system: filter by tag and keywords.
3. utilize the database system: support for the classification of notes and group notes according to folders
4. create unit test for testing database functionality