[FIX,ENH,REF,DOC] Several fixes to search

• Fix imporperly formatted tracker results in search when MySql indexing is used.
• Put tracker main field at the end of "contents" so it's not displayed close to the title.
• Fix title duplication in "contents"
• Partial refactor of isMain fields in trackerlib.
• Type and document large parts of the indexer.
• Fix bug in UserSource looking for non-existent user tracker 0
• Start throwing exceptions when we try to use nonexistent raw id's in factories, this already surfaced serveral minor bugs, and will certainly surface more