Update docs

[nook24]

This PR contains:

• Fix the docs for CHANGE_CUSTOM_*_VAR external commands
• Update *PROBLEMID and *NOTIFICATIONID macros to UUIDv4
• Add new PROBLEM time macros

[nook24]

• Fixed between typo
• Added Dockerfile + Readme to build and run locally using Docker

@sni Could you please check the macro availability of the new *PROBLEM macros? At the moment they are marked with yes in all cases.

[sni]

that's right, they are available all time. Although they probably only make sense for eventhandler or notifictions.