Use new content views

The following replacements have been made:
* New design document name
    - New view name: (conditions) keys => values
        * Full old view name: (conditions) keys => values

* content/
    - by_sessionid: sessionId => _rev
        * skill_question/count_by_session: sessionId => doc
    - by_sessionid_variant_active: sessionId, questionVariant, active, subject, text.substr() => _rev
        * skill_question/by_session_only_id_for_all: (active == 1) sessionId => null
        * skill_question/flashcard_count_by_session: (questionVariant == "flashcard") sessionId => doc
        * skill_question/lecture_question_count_by_session: (questionVariant == 'lecture') sessionId => doc
        * skill_question/lecture_question_ids_by_session_and_subject: (questionVariant == 'lecture') sessionId, subject => _id
        * skill_question/lecture_question_ids_by_session_for_all: (questionVariant == "flashcard" && active == 1) doc.sessionId, doc.subject, doc.text => {}
        * skill_question/lecture_question_subjects_by_session: (questionVariant == 'lecture') sessionId => subject
        * skill_question/preparation_question_count_by_session: (questionVariant == 'preparation') sessionId => doc
        * skill_question/preparation_question_ids_by_session_and_subject: (questionVariant == 'preparation') sessionId, subject => _id
        * skill_question/preparation_question_ids_by_session_for_all: (questionVariant == 'preparation' && active == 1) sessionId, subject, text => {}
        * skill_question/preparation_question_subjects_by_session (questionVariant == "preparation") sessionId => subject
    - doc_by_sessionid_variant_active: sessionId, questionVariant, active, subject, text.substr() => doc
        * skill_question/by_session: sessionId, subject => doc
        * skill_question/by_session_for_all_full: (active == 1) sessionId, subject, text => doc
        * skill_question/by_session_sorted_by_subject_and_text: sessionID, subject, text => doc
        * skill_question/flashcard_by_session: (questionVariant == 'flashcard') sessionId, subject, text => doc
        * skill_question/flashcard_by_session_for_all: (questionVariant == "flashcard" && active == 1) sessionId, subject, text => doc
        * skill_question/lecture_question_by_session: (questionVariant == 'lecture') sessionId, subject, text => doc
        * skill_question/lecture_question_by_session_for_all: (questionVariant == 'lecture' && active == 1) sessionId, subject, text => doc
        * skill_question/preparation_question_by_session: (questionVariant == 'preparation') sessionId, subject, text => doc
        * skill_question/preparation_question_by_session_for_all: (questionVariant == 'preparation' && doc.active == 1) sessionId, subject, text => doc

The following views have been removed:
* skill_question/questions_by_ids: _id => doc (use all_docs)