UX polishing and bugfixes

[zephod]

From Ira: PDF of bugs and suggestions is attached.

Notes from various conversations:

• [dataset/edit]: Rearrange the delete resources mechanism;
• [dataset/edit]: Rearrange the 'you have unsaved changes' warning;
• [dataset/edit]: Are the expand/retract mechanisms sane? Could use arrows, could use pencil, could edit in place... (it's probably fine once the above are done).
• [markdown editor]: Tab colours confuse the user. Inactive button appears to be greyed out.