refactor: fix ESLint warnings & style improvements

[diogogmatos]

• Fixed all ESLint warnings on the platform (most originating from useEffect's without proper dependency configuration).

• Removed the Export to PDF function that has not been functioning for a while now. Before removing it, I fixed it and tried to improve it but the results are just horrible.

• Improved the styling of the buttons in the Sidebar, specifically the Export button, since it now has only 1 function (Export to a Calendar).

• Changed the Calendarium logo to use the CeSIUM's font for it's lettering (instead of manually made letters) while also improving the size ratio of the icon when compared with the text (used the same one Google Calendar logo uses).

• Improved the calendar view selection on mobile by dynamically changing the button icon to reflect the current view.

Before	After

• Improved the way the Calendarium logo and sidebar button are sized on small screens to keep the logo from overlapping with the button.

• Replaced the Ant Design Popconfirm component by ConfirmPopUpButton component to better follow the app's design system and improve overall UX.

Before	After

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