Move some Cursor methods to CursorData

Move some Cursor methods to CursorData

Basically, everything that does not depend on a BufferView should move
there. Some methods that do not seem to need a BufferView, like
selHandle or IdxFirst or push actually depend on it and could not be
moved.

This allows to simplify a few uses of recordUndo helpers.

- Move some methods to DocIterator: nextMath, prevMath, getPossibleLabel,
  getEncoding;

- Move some methods to CursorData: setCursor, setCursorSelectionTo,
  (setCursorTo|normal|reset)Anchor, (set|clear)Selection,
  sel(|ection)(Begin|End), selectionAsString, info, currentState,
  (mark|clear|check)NewWordPosition, fixIfBroken, sanitize, all undo
  related methods, reset, isInside, leaveInset, current mode;

- kill some unused methods: macromode, replaceWord, setScreenPos, touch,
  markInsert, markErase;

- Move code around to group things, and add a few comments (a lot remains to be done).

This changes lead to some related changes in other classes: removal,
change of parameter.

No intended change.