modify underlying component to contain a real text input field for compatibility with name/placeholder setting
handle being set with an empty signature image (store and display nothing)
support readOnly field attribute
change to honor the convention that setValue() and getValue() should use the same values - otherwise field appears changed and record "dirty"
permit dynamic change of signature canvas dimensions
ensure empty signature box (no data) is interpreted the same way as a blank field by detecting blank images
make text of reset/save buttons configurable by the user
Merge pull request #2 from jefftrull/master

Updates for compatibility with Touch 2.2.1