Possibility of defining currencies

[MillhioreBT]

• I have followed [proper The Forgotten Server code styling][code].
• I have read and understood the [contribution guidelines][cont] before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

• Define new currencies or configure existing ones
• The npc bank has been ignored because it treats currencies very specifically and we still do not have a convention of what currencies should be called
• The method Game.getCurrenyItems returns a table with the ItemType of each currency, this table is ordered from lowest to highest , so the first currency will always be the most cheapest and the expensive will be the last
• Added a methods for ItemType and Item, this method is getWorth

Issues addressed: Nothing!