Fix deletion bug

Classic accidental reusage of variable inside a loop meaning that
whichever account you dragged out, the last one in the list would
always be removed.
Refactor + cleanup

Complete rejig of the structure in background.js and cleanup
throughout.
Absolutely no change in functionality, main reason is to prepare for
future updates.
Update copyright year (bit late :)
Update copyright
Refactor v2
Fix account removal bug.

Fixes #3, this must have been due to either a chrome behaviour change
or platform differences. Essentailly using html/text ad the content type
of the drag/drop data caused html tags to be inserted with alongside the
data
v2.2.0