added definition to the top of concept pages

seems like crucial information

of course configurability makes this much harder than it first appears
(cf. inline comment); TBD
moved concept sidebar to the bottom

caveats:
* the "create concept" link is now gone - but it never seemed right
  there anyway, so we need to find it a new home
* eventually, these links should be displayed horizontally
* RDF representations should have dedicated icons:
  http://lab.linkeddata.deri.ie/2011/rdf-logos/
added RDF icons

as permitted by http://www.w3.org/RDF/icons/

caveats:
* should probably be a background image, but I had some trouble sizing
  that properly
* not sure which Sass module this belongs into
introduced view model to move logic out of template

there's a risk that we're just introducing yet more indirections (like
iQvoc needs more of those... ), but it does seem more manageable by
providing a more immedate overview of available properties - however, it
remains to be seen how this approach fares with more complex branching,
as that _might_ lead to awkward duplication and dependencies

for the moment, I opted not to use a separate library (e.g. presenters
via https://github.com/drapergem/draper) as this seems straightforward
enough to not warrant such additional complexity

caveats:
* for some reason `auto_link` doesn't work (cf. inline comment)
* definition class and index are hard-coded (cf. inline comment)
* context (`ctx`) passing should not be necessary, but I wanted to avoid
  `instance_eval` - not sure there's an elegant solution here
* only a few properties have been ported to `@view` so far - eventually
  we probably want _everything_ to go through @view
* that `if...else` for representation icons belongs might seem like it
  belongs into the view model instead - but that would introduce HTML
  into that layer, which seems wrong

/cc @mrreynolds
fixed definition retrieval, guarding against nonexistent records
introduced language-based categorization, starting with labels

the assumption here is that most users are interested in one particular
language (rather than an overview based on the underlying data model)

while the top provides a brief summary (using the selected locale),
these language sections provide a detailed overview (with non-localized
values)
added support for notes

NB: note annotations are currently being ignored
added support for note annotations

not pretty (cf. inline comments), but sufficient for the moment
improved notes styling

unfortunately, the Bootstrap grid induces yet more divitis here
removed obsolete variable
added missing translation

in the process, fixed use of quotes and argument name
ensured the correct language tab is selected by default

not sure this is entirely correct, but it's consistent with the language
selection menu (`app/views/layouts/_controls.html.erb`)
replaced hash with OpenStruct for readability

this significantly cuts down on visual noise

perhaps we should consider a proper `Language` class instead, as that
would make its structure more immediately apparent - but I wasn't sure
how best to name(space) that
ensured definition contents are auto-linked

not sure why this works now, but didn't before
replaced hash with OpenStruct for readability and consistency

cf. 54a0534491c206aabf1747c16dccc3e0ef36454e

in the process, fixed URIs (string vs. symbol)

still seems a bit too implicit/hidden though
added support for collections

in the process, improved documentation and refactored internals

not sure how to handle grid columns given the conditionals, that might
get a bit messy
added supported for related concepts

styling-wise, this doesn't scale - collections and related concepts
should probably be listed inline eventually

headings are currently hard-coded because we (intentionally) don't have
access to the class (thus no `.model_name.human`) and the translation
file appears to have no corresponding entry yet either
replaced OpenStructs with classes for readability and explicitness
started internal refactoring by turning representations into getter

eventually all multi-line calculations should be externalized in similar
fashion

unfortunately though, this means we lose the concise-but-comprehensive
overview at the top

note that this abolishes the setter, which might affect iQvoc extensions
turned definition into getter