LP#1857150: eg-fm-record-editor: add isDirty() method

LP#1857150: eg-fm-record-editor: add isDirty() method

This adds an isDirty() method to the form that components embedding
an eg-fm-record-editor can use to check whether the form is
currently dirty.

NOTE: not all of the custom components that can show up on
      an fm-edit form currently implement component-level
      dirty checks.

Sponsored-by: Evergreen Community Development Initiative
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Ruth Frasur <rfrasur@library.in.gov>
Signed-off-by: Bill Erickson <berickxx@gmail.com>