#702 Check for valid characters

[Ken]

Sometimes when I copy and paste values for the various fields from a PDF or the web I get characters which subsequently cause errors when I try creating a PDF through LyX. For instance, there appear to be various types of hyphens or dashes. Some are virtually indistinguishable to the eye but cause problems on when compiling a LaTeX document. Other characters need to be escaped. For instance, the ampersand should be \& and not simply &. Lastly, sometimes I might include LaTeX math commands but forget to encapsulate them between $..$.
It would be nice if JabRef could:
(1) search for illegal characters
(2) search for un-escaped characters
(3) search for LaTeX math with potentially needs to be wrapped in $..$

The last one might be less important/useful.

Note, however, when searching for (1) and (2) only particular fields are likely to need checking or some fields might require different checking rules. For instance, checking the URL/DOI/filename field would require different rules than checking the authour/title/abstract fields.