URL placeholders handling, and find pattern syntaxes

To improve URL placeholders.

Used in:
- find query, replace query in URL placeholder
- i4k-find-info replace placeholders with highlighting

Ideas;
- named placeholders
- "placeholder pattern language" like w3c OWL, to describe the URL and what it can accept (and interpret more the user query, or give it a syntax to accept "named arguments somehow", maybe by combining multiple queries
- https://api.github.com/search/repositories?q=fork:true+topic:i4k-find+topic:package+ has already placeholder in the URL, made for humans, but could be used to gather info
- filling placeholders during suggestions
- placeholder data types, could be stored with the pattern
- `i4k-find:///` when info could be describing the URL and expected output (from the app, its actions and accessible/forwarded data)