use treeview helper
moved collection-specifics into the corresponding class

not entirely sure this is correct, but it's hard to tell from history or
test coverage
fixed collections' concept members not being clones
add code coverage tool.

* Run code coverage with: `bundle exec rake test COVERAGE=1`
* Find results in coverage/index.html
deactivate jqtrees contextmenu event (fixes #314)
ensured consistent margins in treeview

crude, but seemingly effective
tweak simplecov config
Merge branch 'master' of github.com:innoq/iqvoc
fixed partially hidden datepicker

jQuery UI automatically sets the z-index to be higher than the
originating field (though that's not well-documented), so we set a
sufficiently high initial value there
fix language selection controls
fixed error messages
simplified internals for readability
Revert "simplified internals for readability"

accidentally committed an unrelated change

This reverts commit a6db9842e539de7732315878e7def50deca4360e.
simplified internals for readability
fixed existing subcollections being omitted in edit form
fixed EntitySelector rendering on Safari

note the inline comment
simplified internals, improved consistency
removed ancient debugging remnants
ensured autocomplete fields do not accidentally trigger form submission

this seems crude and something that jQuery UI should include, but
apparently not - at least not in the current version
upgraded jQuery UI

general maintenance; includes various bugfixes (though nothing in
particular)

as before (cf. 400aa9a641bffb16399548900d60c509f9f049e5), the upgrade
docs have not been updated because the procedure likely isn't stable -
also, original CSS files were modified to add `.scss` suffix and replace
`url(...)` with `asset-url("...")` (except for `data:` URIs)