Show a guide on how to create proposals

[bluec0re]

Is your feature request related to a problem? Please describe. First time users currently have a hard time to know how to create a proposal.

Describe the solution you'd like Add text box to the proposals page if there are no proposals yet and describe the process.

Describe alternatives you've considered

• Hide the proposals menu entry if there are no proposals to avoid confusion
• Add a "create/+" button which redirects to the start page with the search box focused.

@felixwilhelm