Add doors

[slemonide]

There are two types of doors:

• Open doors that will open automatically as player tries to walk through them.

• Lockable doors that require a key to open them

• Lockable doors that do not require a key to open them, but they could only be opened/closed from one side

• Weak lockable doors that can be broken with some heavy tool

• [x] Open doors

• [ ] Key lockable doors

• [ ] One-side lockable doors

• [ ] Key + one-side lockable doors

• [ ] Weak doors

Open doors:

• [x] Make them visible
• [x] Update Tiled support
• [x] Make them solid
• [x] Make them open
• [ ] Change the trigger size dynamically