New items to collect + backpack

[ppedziwiatr]

1. All items should be collected in the backpack
2. Backpack should have X slots. Each slot can contatin 'Y' items of the same type. 'X' should depend on the beaver type, eg

• heavy beaver - x: 5, y: 5
• tech beaver - x: 4, y: 4
• agile beaver- x: 3, y: 3

3. New items:

• token/mines scanner - scans all the nearby fields for hidden tokens (eg. tank and agile - 2 fields range, tech beaver - 3 fields range)
• teleport - teleports the beaver to a random field on map (as a good way of running away from a fight)
• mines - mines are hidden, moving on a field with a mine reduces hp. If a player gets killed, the player how placed the mine is rewarded
• "quad damage" - increases damage for X rounds
• "aerial attack" - attacks multiple beavers around the player