Allowed to repeat the same key when binding a control

[Lonami]

You can repeatedly bind the same key to any control:

Steps to reproduce

1. [ESCAPE]
2. Options
3. Input → Controls
4. Keyboard configuration → Configure
5. Custom 1
6. Left click on any option, press any key
7. Repeat step 6

Expected behaviour

I shouldn't be allowed to do as shown on the attachment…

Actual behaviour

…But I am allowed.

[Riot]

prevent binding the same control to the same key or button multiple times, resolves #303

→ <<cset 2afe4af762ba>>

[Riot]

Removing milestone: Beta (automated comment)