resources can say where they want to go

when a resource is a double [newpath,currentpath], the file loaded from `currentpath` is placed under `newpath` in the exam'sresources directory.
Merge branch 'images'
add compiler option to minify javascript

`--minify <cmd>` will run <cmd> on all javascript files.
Concatenating scripts would be even better, but I need to start using a proper script-loading system for that to work.
Merge branch 'master' of github.com:numbas/Numbas
Merge branch 'master' into feedback
title attr on feedback icons; fix m_n_x tickers