Pfeifer/proof mgmt includes fix

[WolframPfeifer]

This PR adds a small feature (for use in an ongoing case study by @FliegendeWurst) to the proof management command line tool: It allows using also the check for missing proofs when the specification in the source file contains dl_ escapes, and thus for loading them a project.key file is needed. At the moment, only this file (top-level in the proof bundle to load) is considered, the includes are read from there.

Type of pull request

• New feature (non-breaking change which adds functionality)
• There are changes to the (Java) code

Ensuring quality

• I made sure that introduced/changed code is well documented (javadoc and inline comments).
• I have tested the feature as follows: Manually with a small example

The contributions within this pull request are licensed under GPLv2 (only) for inclusion in KeY.

[WolframPfeifer]

@FliegendeWurst Can you check if this works for your case study? It should read the top-level project.key file in the bundle, and consider all the includes from there.

[FliegendeWurst]

Works for my project 👍