Support for project functions

[ZdenekM]

• Alternative to a composed action (user-defined method of service or object composed from already existing actions) - function defined within the project (main script).
• Suitable for a code that is used multiple times but could not be generalized to be used in more projects.
• Benefits: simplifies main script code, reduces code duplication, improves readability, the well-known pattern for programmers.
• JSON representation will reuse the data structures used to represent project-level actions and logic.

Current state: prepared data structures, no support at all.