D3bootstrap delsec

[jorisvanzundert]

This one implements #10, deleting of sections.

Tests to be added:

• add a section
• then delete it
• then delete a pre-existing section
• rerun all other tests (there should be no side effects)
  • esp. order of sections shouldn't be affected
  • ordering should still function
  • editing sections should be unaffected
  • etc.