SubmissionCollection moves

[Alberth289346]

Introducing a SubmissionCollection and moving common part of submission parsing to Submission.

This is stacked on top of #230 but much bigger, and it may need some tweaking or discussing before it's good. Don't merge before #230 I'd say.

As explained in #230, I am having a fight with Java versions and maven.

I didn't do testing beyond running maven that includes some tests.

[Alberth289346]

Apparently it throws #230 and this patch onto one heap of changes, making the changes unreadable :(
Don't know how to fix other than wait until #230 is merged,

Marked it as draft to avoid accidental merge, however if you're happy with the changes, feel free to convert it back to ready.

[tsaglam]

Maybe you can update the PR, now that #230 is merged.
Also, note that I turned the our discussion regarding submission filtering into issue #232, which might be also relevant for this PR.

[Alberth289346]

New version, less involved than the previous try.

I contemplated whether to move the JPlag parsing code into SubmissionSet, but that likely isn't going to be very useful with all the links back to the Program interface of the JPlag class.

[tsaglam]

I contemplated whether to move the JPlag parsing code into SubmissionSet, but that likely isn't going to be very useful with all the links back to the Program interface of the JPlag class.

I like the changes in this PR. I checked out this branch and I think I found a way to reasonably move most of the parsing code into the submission set (basically separating the error reporting capabilities defined by Program into an own class). I will try to fully implement that on top of your changes and then we can maybe discuss them here.

[Alberth289346]

WIP: https://github.com/Alberth289346/jplag/compare/subm-collection-moves...Alberth289346:frutsel-program?expand=1

I had a go too, created a new ProgramProxy, acting as Program for the language parsers, then started hacking the implements Program out of JPlag. Also pulled Language language out of options as I didn't see much need for it there, but report now dies :p

[tsaglam]

I had a go too, created a new ProgramProxy, acting as Program for the language parsers, then started hacking the implements Program out of JPlag. Also pulled Language language out of options as I didn't see much need for it there, but report now dies :p

I also removed the error collecting from the program and changed the language frontend dependencies to no longer reference the main class. However, I think it is better to leave the language in the options, due to other features that are currently worked at. These changes do not affect the report generation. Maybe you can take a look at #234, if it is okay with you I would go ahead with that approach (so first merge #231 and then #234).