Add issue form for user stories

[MakisH]

Closes #283 #134 #33.

Looks approximately like this:

After merging (to understand what form the link will have), I will also update the note on the community projects page.

Unfortunately, issue forms do not support images at the moment, but I assume one could attach them in a follow-up comment. One probably needs a GitHub account anyway, but does not need to know how to open a PR and which files to change.

@uekerman is this all we need for now?

[uekerman]

I always used this mail template

Title (ideally related to your application/ your research, not the coupled codes etc.)
Text (max characters including spaces 800)

• Which application?
• Which solvers have you coupled?
• Why have you used preCICE?

Name,
Affiliation,
Link to profile (optional),
Link to publication (optional)
Picture (ideally high resolution)

[MakisH]

Refined, now looks approximately like this: