Multifile2

[jankapunkt]

This implements multiple file uploads using a multiple Boolean flag in the schema or field config, as discussed in #3 long time ago.

It allows the operating system's file selector to select multiple files, adds these files to a reactive queue and uploads them one-by-one. Uploaded files get assigned a plus Button (as typically in list based Autoform elements).

• Make sure you're using spaces for indentation
• TBD: Make sure all new code is documented in-code-docs
• Make sure new features, or changes in behavior is documented in README.md
• Make sure this PR was previously discussed, if not create new issue ticket for your PR
• Give an expressive description what you have changed/added and why
• Test regression
• Test full functionality (add, delete, replace, mix of these three)
• Test backward compatibility

[dr-dimitru]

@jankapunkt thank you for your contributions and support over this reps.
Let me know when this one is ready to get merged

[dr-dimitru]

@jankapunkt let me know if you think it's good to merge as it is. Any plans to push more changes?