Added feature for full screen

[RigvedRocks]

What does this PR do? I have added the functionality for the full-screen feature as outlined in #202

Changes I have added the full-screen feature to the project. In this I have made modifications to the following files and folders - i) Added two new files in the Icon folder for full-screen and exit full-screen icons - FullScreen.tsx and ExitFullScreen.tsx ii) Made changes to the HeaderTimer.tsx iii) Create a new file named fullscreenStore.tsx in the store folder.

Screenshots or GIFs (if applicable)

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• I have reviewed my code and believe it is ready for merging.
• I understand that this PR may be subject to review and changes.
• I agree to abide by the code of conduct and contributing guidelines of this project.

[RigvedRocks]

Thank you so much for the insights, bryanlundberg. Based on your suggestions, I have modified the code. Please have a look at the latest commit and suggest amendments if any.

[RigvedRocks]

@bryanlundberg Can you please guide me as to how I can just merge the hooks and icons. I am new to the field of open-source development. Sorry for the trouble. If you want to I can close this draft PR, and open a new one with the hooks and icons.

[RigvedRocks]

Closing this draft PR and opening a new one, merging the hook and icons along with changes to the timer component.