PassByClue: Match clues case-insensitively

What a silly mistake.
PassByClue: Also allow -ed, -ing suffixes in document title
Solr: Do not include non-required terms in proximity queries

(Note that this is a nop right now because all terms are marked required;
this will change in upcoming commits.)
QuestionTypes Clue: New isReliable feature controlling SolrTerm.isRequired

(So far, it is always true so this is a nop, but this will change
momentarily.)
CluesToConcepts: Mark ClueConcept as unreliable

Some of the redirects are weird so we cannot blindly require the
rewritten label to be present.
CluesToConcepts: Remove even the original clue, create ClueNE instead

The original clue might have been a CluePhrase which gets ignored during
search; since we also remove all sub-clues, that means the concept will
get *completely* ignored during full-text search, not good!  So create
a ClueNE that will represent it for that purpose.
CluesToConcepts: Create ClueNE only when concept label is reworded

Unconditionally creating ClueNE meant that we often (when there
was no redirect involved in the concept) had two redundant clues,
which then messes up weighing and Solr's search results.

Therefore, we now create ClueNE only when rewording happenned to
keep carrying the original text, and otherwise simply mark the
ClueConcept reliable.
CluesMergeByText: Always prefer reliable clues