Epic: Block composition & organization

[ApocDev]

Make blocks easier to structure and arrange: reorder rows to match how a chain is actually thought about, collapse a long chain into a nested sub-block, and organize blocks into nested folders.

Sub-issues:

• Block view: drag/drop to reorder recipe rows #6 — drag and drop to reorder recipe rows within a block.
• Sub-blocks: collapse a multi-step chain into a nested block #7 — sub-blocks: collapse a multi-step chain into a nested block.
• Sidebar: nested folders (folders inside folders) #8 — nested sidebar folders (folders inside folders).