HPCC-10816 Add back/forward support to GraphWidget

Add back/forward support.
Improve caching of layouts.
Allow main graph to view "localised" graphs.
Improve "safe" mode.
Search now includes IDs.
Improved icons.
Replaced "../files" with "/esp/files"

Fixes HPCC-10816

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>