Self-Defined Links in Navigation: Users should be able to add self-defined Links

[iaktern]

Users and Organizations should be able to add self-defined, external Links in the Navigation Panel under the Space Settings:

• For personal spaces: add a settings area like in organizational spaces. Call the parent navigation element "Your Space" and the child "Settings". Use the same icons like for organizations.
  
• In Settings, add a way to add multiple external Links. For example, maybe like we add Custom Properties in the BPMN Editor. With a input fields for 1. the "Descriptive Link Name", 2. the "Link Address", 3. Selection field to select an "Icon" out of a list of predefined icons
• Validate that the input is a valid URL (just the syntax, not if it is reachable)
• Store the links in the DB
• Add every stored link in the Navigation pane under "Your Space"/"Organization". The order/sequence should be the order in the settings menue.