Remove Recursive save_collection strategy

[slemrmartin]

rebase of #20, solving conflicts with #19

[slemrmartin]

cc @agrare

[slemrmartin]

@Ladas, @agrare: helper for this review :)

diff makes sense only with param w=1 in url. To see it in large diffs, which are hidden under "Load diff" anchor, use these steps (in Chrome):

• Right click on "Load diff", click Inspect
• Find parent tag named <include-fragment>
• This tag has attribute "data-fragment-url" - add w=1 param to this url
• Then click to Load diff