refactor: move helper functions into getters (#318)

* refactor: remove getExternalBorders helpers function and calculate values in the getter

* refactor: remove getBorders function and put it in the getter

* refactor: remove perimeterInfo as helper function and put it as a getter

* refactor: remove internalIDs as a helper function and put it as a getter

* refactor: remove boxIDs as a helper function and put it as a getter

* refactor: remove getHolesInfo as  a helper function and put it as a getter

* refactor:replace getMap() with map property in functions that were turned into getters

close: #315

Author: EscapedGibbon