using fork_of for showing the parent notebook
Merge branch 'develop' into issue-115-reworked-0.2
changed forked from display
Merge branch 'pr/894' into develop

Conflicts:
	htdocs/editor_tab.js
fix refactor mistake
fix typo in refactor
place and style fork description
augment notebook with fork_of, instead of storing as notebook cache field

various proliferation of fork_of defeated
add link to fork parent from description
super-hacky set of notebook property `fork_of` when forking one's own