refactor handling of sibling navigations

* make the max number of the scored entries for performance
* create a list that has just enough items to display
* move the constant for the max number of siblings from the global settings
  to the internal settings
refactor handling of navigation links

* create a list that has just enough items to display for performance
* apply the displaying limitation to the page information too
* move the constant for the max number of items of each type from the global
  settings to the internal settings
* remove the display of 'count/total' from |kFormat.tooManyItems| tooltip
minor fix

* arrange the name of variables
* use |let| and |const| instead of |var|
* edit comments
* add new lines for formatting