feat: Offline support

[techno-disaster]

Description

Adds offline support to app so that user can view tasks and other functionality in app when not connected to the internet too :)

Fixes #129

Flutter Channel:

• I have used the Flutter Beta channel on my local machine

Type of Change:

Delete irrelevant options.

• Code
• Quality Assurance
• User Interface

Code/Quality Assurance Only

• This change requires a documentation update (software upgrade on readme file)

How Has This Been Tested?

Physical device, uploaded on youtube here
I could not get the gif under 10mb so I would suggest you download the app from the pull requests artifacts and test it.

Checklist:

Delete irrelevant options.

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged

Code/Quality Assurance Only

• My changes generate no new warnings

[techno-disaster]

Resolved merge conflict. @anitab-org/coding-team can someone give this a quick review?