UI help: Escape the special symbols

[NChechulin]

Is your suggestion for improvement related to a problem? Please describe.
JabRef doesn't seem to escape special characters (\% instead of %), and this results in LaTeX projects not building.
Although it's not really a JabRefs' fault, it would be great to have this kind of things managed automatically.

Describe the solution you'd like
JabRef automatically alters all the text fields so that all the special symbols are escaped.

[Siedlerchr]

Hi, Jabref has a cleanup for this you can enable: https://docs.jabref.org/finding-sorting-and-cleaning-entries/saveactions#latex-cleanup

You can also enable it as save action

[koppor]

In other words: Give the user hints where something is wrong. Older JabRef version had this checks (red cells in the entry table). Current JabRef sometimes has an exclamation mark in the field editor.

Refs #6856