Issue content convention

[sadikkuzu]

Let's indicate appropriate requirement for each issue if possible.

i.e.
Requirement: F-2.9
Requirements: F-2.9, F-2.11
etc

And
Let's not specify Due Date in the end.
Let's use project card in order to keep Due Date in date resolution.

To sum up, for this issue example:

before

@frontend The professor didn't like how our pop-up error messages looked during the presentation.
Let's fix them for the web app, and design them for mobile as well.

Due Date: Milestone 2 Presentation

after

@frontend The professor didn't like how our pop-up error messages looked during the presentation.
Let's fix them for the web app, and design them for mobile as well.

Requirements: F-1.1, F-1.2