ENH: add IOobjectList::findObject() method

- naming similar to objectRegistry, with unambiguous resolution.
  The lookup() methods have different return types depending on the
  calling parameter.

STYLE: use IOobjectListTemplates.C for implementations

- previously included as local definition within IOobjectList.C,
  but will be adding more templated methods soon.

- adjust parameters (eg, matchName instead of matcher) to show their
  function

ENH: handle objectRegistry::names<void>(...)

- this is equivalent to no Type restriction, and can be used when
  filtering names. Eg,

     obr.names<void>(wordRe..);