Create Toggleable skills

[NeumimTo]

• In skilltree config only
• option which makes the skill toggleable

   id: "ntrpg:toggleable_thunderbolt"
   parent: "ntrpg:thunderbolt"
   Settings {
      blablabla
   }
   Toggleable {
      period: 10000
      max_duration: 100000
   }

What will actually happen on the backend during skilltree initialization:

1. create a bytecode for a skill via asm (similar principe as skill with type of "item-access", "command" etc),
2. When the skill is casted it places a buff (effect) to the caster which executes the "parent" skill every X ms

• In toggleable block only period is mandatory.
  Another possible options:
  max_duration - if not specified skill will run as long as character has enough mana